How Gray Water Reclamation Works

To understand how gray water is absorbed by soil and plants, imagine emptying your backpack on the subway. That pile of stuff is much like gray water. It consists of various items that are useful or useless to the environment you introduced them to. There are certain items that will lie untouched — perhaps your smelly gym clothes or a really boring book. Plants and soil are much like the other train commuters. They’re ready to snatch the items they have the most use for and leave the less attractive ones behind.

Plants and soil work hard to break down gray water. Soil filters out many contaminants through a basic process:


  • ­As water passes through layers of sand or granulated rock, larger water contaminants are caught in the grit of the dirt’s solids. This process is like straining solids out of soup with a colander, on a smaller scale. (If this sounds far fetched, remember that one key component in commercial water filters is charcoal.) The dirt itself helps filter out nutrients and biodegradable materials, which can then be absorbed by plants and bacteria.
  • Microorganisms and bacteria in the ground feed off of carbon and pathogens, leaving water, carbon dioxide and non-polluting insolubles.
  • The rest of the water, now purged of major pollutants, is absorbed by plants or seeps down to recharge the groundwater.

It’s important to remember that plant life varies greatly, and some species are unable to deal with the chemicals, salt or acidity levels in gray water. Other plants just call for careful watering and care to begin with. In many situations, drainage from kitchen sinks and dishwashers is too contaminated by grease and high acidity to be used at all.

Even without coming into contact with human waste or strong chemicals, gray water can contain food particles, grease, bacteria and some pathogens due to contact with our food, soaps and bodies. The yard can handle these elements, but that doesn’t mean you can.

Take care to prevent gray water from coming into contact with any fruits and vegetables due to the contamination risk (especially if the produce may be consumed raw). Fruit and nut trees are generally considered safe picks due to the distance between the ground and the food, but all other food gardens are best irrigated with white water or rain water. Additionally, gray water usage should be suspended altogether when a household resident is sick, as this only increases the contamination risk.


To further prevent contamination, don’t store gray water for reuse. If allowed to sit, gray water quickly turns into a stagnant, sludge-filled concoction of bacteria and pathogens — these elements thrive on some of the same nutrients a garden could benefit from. This feeding frenzy needs to take place in the soil, as described above, not in your tank. If gray water is collected and stored without treatment, it effectively becomes black water in as little as 24 hours.

But what kind of system gets all that gray water out to the garden? How much is the installation cost? It can all be as simple as grabbing a bucket.


What Are the Effects of Soapy Water on Plants?

soap container image by timur1970 from

As an ecologically responsible gardener, you want to conserve water and avoid introducing toxins into the environment. But not all toxins are labeled as such. Detergents labeled “non-toxic” may be harmless to the environment at large; up close and personal is another story. Get the facts before soaping up your garden.

Kill Your Garden

Soaps and detergents are toxic to plants. A strong solution of soapy water sprayed onto foliage can disintegrate the leaves’ waxy coating, resulting in water loss and the eventual dehydration death of the plant. And though it may seem like a good drought-conscious practice to water your plants with the soapy water left over from washing the dishes, your plants will pay for it in the long run. Soap will remain in the soil, making it toxic and eventually deadly.

Control Weeds

Soap isn’t picky. It’ll kill the plants you don’t want as surely as the ones you do. To make an herbicide that will do in your weeds without damaging the environment, mix 5 tablespoons of dishwashing liquid or liquid hand soap into a quart of water. Coat weeds well and soon enough they’ll wilt. This method works best when it’s hot out and plants are most susceptible to dehydration.

Control Pests

You may be wondering why anyone would want to spray soapy water on garden foliage. Mites and aphids are two very good reasons. Soap kills small, soft-bodied insects the same way it can kill plants: it penetrates and dissolves the protective wax coating the insect, and they lose water. It can also disrupt the insects’ cell membranes.

If you want to exterminate pests without hurting your garden, use horticultural insecticidal soaps, not homemade detergent solutions. Horticultural soaps contain ingredients selected to maximize damage to specific insects and minimize damage to plants. They’re a lot more consistent from batch to batch, too.

Always dilute insecticidal soaps according to the label instructions. Every four to seven days, spray plants thoroughly, including the undersides of leaves. Only those insects you coat when you spray will die; those that arrive later will be unaffected. To be safe, spray a test area of a small plant and wait a few days before applying it to your whole garden; some plants are more sensitive than others. And use the spray only during the cooler parts of the day, for the same reason you’d use soapy herbicides when it’s hot out: plants are more vulnerable to dehydration in the heat.

Garden Myths – Learn the truth about gardening

Do you want to start an online fight? Ask about using using gray water in the garden (also spelled graywater, grey water and greywater). Opinions vary widely, and both users and non-users feel very strongly about their position. You will see lots of opinions, and many statements that are false.

In highly developed countries there is a definite distrust of gray water, but as regions experience more drought people are starting to consider it as a viable option. Clean water, also called potable water, is wasted on landscapes and as the cost of it goes up, more and more gray water will be used. In this post I will discuss its use in the garden.

Is Gray Water Safe for the Garden?

What is Gray Water?

Such a simple question and yet we can’t agree on what it is. It does include water collected from laundry machines, bathroom sinks and showers. Some people also include water collected from the kitchen sink, while others don’t.

Water from the toilet is called black water and some include kitchen sink water in this category.

Why can’t we agree on a definition? Because politics is part of the story. Each government, federal, state, provincial and municipal wants to have their own definition. Government is not smart enough to standardize.

In this post I will consider grey water to exclude the kitchen sink and call this ‘kitchen sink water’.

The Yuk Factor

Imagine eating vegetables being watered with the same water that you bathed in? Yuck! For some reason we find this unacceptable.

But consider this. What gives that tomato its great flavor? Worm poop. Rotting vegetation. Bird droppings. Dead mice. Thousands of different dead insects.

Gray Water and the Law

Each level of government has different rules about graywater. In some places it is illegal to use it in the garden – dumb, I know, but that is the way it is. In other places you are not even allowed to collect rain water for use in the garden.

Other areas allow you to use gray water, but only after it has been treated. This seems to be common, here in Canada, where the focus is on adding large gray water cleaning systems to homes. The only problem is that they are too expensive, especially since our water is still cheap. So nobody uses them. But I doubt police will be checking how you use gray water.

In some places you are free to use gray water anyway you want, but most jurisdictions have some regulations that you should check before using it. Or at the very least – don’t tell your neighbors what you are doing. 🙂

Understand your local laws.

Concerns About Gray Water

There are two main concerns about using gray water in the garden; chemicals and bacteria.

Gray water contains numerous chemicals but the main ones will be the cleaning products added during the washing process.

Bacteria are a concern because they can cause infection and disease. It is unlikely that they will affect the health of the plant, but if these bacteria return to humans or pets they could conceivably cause problems. Remember that our bodies are covered with bacteria and fungi. As we wash, some of these are washed off into the gray water. If you wash some fruit, you will add microbes from the fruit. Even standing water collects microbes from the air.

A main concern for bacteria comes from the fact that fecal matter entering gray water could cause diseases.

A third concern is the pH of graywater.

Chemicals in Gray Water

Certain chemicals will harm plants. The ones of concern with gray water include sodium, boron, and bleach.

Sodium and boron are commonly found in soaps and detergents and even low levels are toxic to plants.

A lot of on-line advice suggests that you use gray water in the garden, you should only use soap and not detergents. This advice doesn’t make any sense since soaps such as dish washing soap are actually detergents.

Both soaps and detergents can contain sodium, which will harm plants. The best option for a cleaning product is one that does not contain sodium or boron. It could be a soap or a detergent.

Keep in mind that we don’t normally use a lot of cleaning chemicals. Consider how much you use when washing your hands compared to the amount of water. These chemicals get diluted quite a bit.

Consistent use of grey water does show an increase of boron and surfactants in soil. Excess sodium tends to wash away with rains, but can be a real problem in some types of soil in arid regions.

Most other chemicals in cleaning products are organic in nature, meaning they contain carbon – this has nothing to do with organic gardening. This means bacteria in the soil will decompose them and turn them into CO2 and water. In low concentrations they are not an issue.

Since chemicals can harm plant leaves, the gray water should be applied to the soil and not directly on the plant.

Bacteria in Gray Water

All gray water will contain a wide variety of bacteria. Most of these will not harm animals or plants. A few can make us sick, but will probably not harm plants.

When soil treated with clean water and treated gray water was analyzed, various pathogens and fecal indicator bacteria, including Escherichia coli, Klebsiella pneumoniae, Salmonella enterica, Pseudomonas aeruginosa, Enterococcus faecalis, and Shigella spp., were found. The reality is that these pathogens already exist in your garden even if you don’t use gray water.

As grey water stands, the bacteria will start to multiply making a potential disease issue worse. Many gray water regulations require you to use the gray water within 24 hours, if it is not treated.

If gray water is added to ornamental beds there is no health risk. Any added bacteria will need to survive their new environment and compete with the bacteria already there. Human pathogens don’t live that long in soil. Since we don’t eat ornamental plants, there is no risk to us.

When lettuce, carrots, and peppers in a greenhouse were treated with gray water containing high levels of both fecal coliforms and fecal streptococci (averaging 4 × 105/100 mL and 2,000/100 mL, respectively), “no significant difference in contamination levels was observed between crops irrigated with tap water, untreated greywater, or treated greywater. Contamination levels for all crops were low and do not represent a significant health risk”

Adding gray water directly to soil will not cause a pathogen problem in plants like tomatoes or beans which have their fruit above ground. Pathogens will not enter the roots, and migrate into the fruit.

There is a potential problem with pathogens attaching themselves to root crops. When you eat the root crop, you could be ingesting some pathogenic bacteria unless you wash and cook it before eating. If you eat the crop right in the garden, or prepare it fresh there is a very minor potential problem.

But consider this. Soil contains thousands of different types of bacteria and we don’t even know what they all are. We do know pathogens are present. People have been pulling carrots out of the ground, wiping them on dirty pants and eating them raw for thousands of years. We are still alive.

Authorities can’t take any risk so they tell you not to use gray water on root crops, but the reality is that the risk of doing this is very low and it is common practice in many parts of the world.

The pH of Gray Water

Gray water tends to be more alkaline, mostly due to the soaps and detergents in the water, but that is not always true. In one study the clean well water had a pH of 7.7 and the gray water had a pH of 8.2. In another study gray water had a pH of 6.7 with clean water at 7.6.

Several studies, but not all, show an increase in soil pH when only gray water is used. The degree of change depends on the pH of the gray water and on the type of soil being tested. Changes in pH will be less dramatic where rain adds a significant contribution to watering. Higher microbe activity in the soil will also mitigate such pH changes.

What About Kitchen Sink Water?

The problem here is that this water contains more bacteria and food particles than normal gray water. The bits of food make bacteria grow faster so there is more potential for pathogens.

Where do the bacteria come from? Some come from your hands, but these are also found in other types of gray water so we can dismiss them as an issue. The rest come from the food we wash. Running water over a carrot or apple before you eat it will add various microbes to the water. But these will be mostly plant microbes – not human ones, so they are less likely to be human pathogens.

When you water a vegetable crop from above it also dumps huge numbers of plant microbes onto the soil. Is this any different than washing some lettuce leaves in the sink and dumping the resulting water onto the soil?

The other issue with this water is that it contains fats, oils and grease. These decompose very slowly in soil, and too much in the garden could be a problem. A lot depends on how much grease you dump down your sink and how big your garden is.

The concerns over kitchen sink gray water are highly exaggerated provided the water is used right away. Storing this water without cleaning it first is more of an issue.

Other Myths About Gray Water

Laundry Machine Water Should Not Be Used

Some people recommend that you don’t use water from laundry machines because the plastic microfiber from the synthetic clothes causes drainage issues in soil. It is true that micro-plastics are being found everywhere and it would be best to keep them out of the environment. But our sewage cleaning systems do not filter them out very well and they end up in rivers and oceans where they probably do more harm than in soil.

They degrade in soil very slowly and plants will not absorb them. They won’t end up in your food.

I doubt that they will change soil drainage conditions, except maybe if they are used over a very long period of time. The plastic is consumed by things like earthworms, which are then eaten by larger animals. We still do not know what harm they do once in animals.

Microfibers are an issue – we just don’t know how big of an issue they are.

Biodegradable Soap is OK

To many people ‘biodegradable’ means that it is perfectly safe. That is simply not true. Biodegradable means that microbes decompose it until finally it is in its basic elements. But as it is decomposed, it can actually be converted into harmful chemicals.

Almost all the soaps and detergents are biodegradable – even if it does not say so on the container. Even crude oil is biodegradable. Products that are labeled biodegradable and contain a lot of sodium, are worse for the soil than non-biodegradable ones with less sodium.

Washing Soda is a Safe Soap

Washing soda is not even a soap – it is a salt.

Washing soda has been used for many years and considered by many to be a very safe product, and it is. The problem is that it is sodium carbonate (sodium, carbon and oxygen) and sodium is very toxic to plants. So this is not a good product when collecting gray water.

Don’t Spread it on the Surface of the Soil

One person commented that you should not spread it on the surface of the soil because you will get flies.

Some regulations require the gray water to be applied below the surface of the soil. I guess this might reduce the chance of some gray water splashing onto plants, but that is hardly a concern. Mulch will also prevent this.

It won’t create flies. They might come for a drink if you spread it on the surface, but so will bees and butterflies.

Gray Water Does Not Contain Fecal Matter

A common definition of gray water is, “all wastewater that is generated in household or office building sources without fecal contamination“.

That is not true. Shower water and washing machine water both contain fecal matter from our bodies and our dirty cloths. In one study, faecal coliforms (CFU 100 mL– 1) had a value of <1 in clean water and 1,000,000 in gray water. You are not as clean as you think.

The same study found that faecal coliforms did not survive long in soil, so it is not really a big issue.

Don’t Use it on Acid Loving Plants

It is a common belief that gray water is alkaline and therefore it should not be used on acid loving plants, like rhododendrons and blueberries.

Gray water is not always alkaline and even if it is, it does not mean it will make the soil more alkaline. If it does not make the soil alkaline it is perfectly fine for acid loving plants. Exercise some care and consider measuring your soil pH.

How Does Gray Water Affect Plant Growth?

Gray water contains nutrients that plants need. Many soaps contain phosphorus. Organic matter will contribute nitrogen, sulfur, calcium, magnesium, iron and other nutrients. Soaps that don’t contain sodium will most likely contain potassium. Gray water is a fertilizer.

How does this affect plant growth?

A study that looked at this issue found that gray water improved growth and productivity of carrots, peppers, spinach and beets compared to clean water. In some cases growth in gray water was as good as or better than with fertilized water. This testing was done in pots.

Gray water grows more peppers than clean water, image from reference 1

Field testing in Texas showed that gray water (laundry water) increased production in bell peppers, Chile and tomatoes when compared to clean water. Gray water did not increase salt accumulation, but did increase pH.

Greenhouse testing showed tomatoes grew better in gray water than in tap water, and those grown in gray water had higher levels of P, K, Ca, Mg, Na, Fe and B.

Other studies have found no increase in productivity, but none reported a decrease in productivity.

Should Gray Water Be Used?

From both a healthy garden perspective and from an environmental perspective, the answer is clearly yes.

Gray water, as well as kitchen sink water, should be used on ornamental beds and lawns. Gray water can certainly be used on non-root crops and can probably be used on root crops without concern. It is certainly safe on root crops that get cooked.

Follow these suggestions.

  1. Don’t store gray water for more than 24 hours.
  2. Don’t use gray water on vegetables if someone in the household has a serious pathogenic infection.
  3. Use cleaning products with lower sodium and boron levels.
  4. Use smaller amounts of cleaning products.
  5. Spread the gray water around your whole yard – don’t keep dumping it in the same spot.

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Irrigating With Gray Water

In order to save money and eat better quality food, I grow my own vegetables (as do many people these days). I recycle the “gray water,” used liquid that does not contain human waste, from our washing machine and kitchen sink by irrigating the garden with it. Is this a safe practice? I assume that, with the new “no phosphorus” soaps, this setup won’t harm my plants or be dangerous to the environment.
Sounds good to me, but you need to keep a few key points in mind. First, your city, county, or state health department will likely oppose your practice, since they may confuse it with black-human waste-filled-water, which can contain pathogens that cause sickness, or even death. (If small children live nearby, you can surely expect such opposition.) Second, some gray waters do contain pathogens (bacteria and viruses) from washed diapers, underwear, and similar items. So use caution appropriate to the origins and composition of your own kitchen and laundry waters. Third, I strongly recommend against using gray water directly on edible crops, particularly on ones that will be eaten raw or slightly cooked because of the risk of contamination.
On the positive side, using household gray water for corn, grains, fruit trees, and lawns makes a lot of sense in almost any climate. Rather than broadcast or spray the liquid, though, trickle the water directly to the plant roots through a “soaker” or perforated hose.
Since phosphorus is an essential nutrient for vegetation (all commercial fertilizers contain the element), I’d recommend that you go ahead and buy phosphate-based detergents, instead of non phosphate types based on carbonate or-especially-silicate buffers. Read the package to know what you’re going to be putting on your lawn and garden.

— David Burmaster, consultant on surface- and ground-water quality and hazardous waste management

What is gray water, and can it solve the global water crisis?

Using gray water is certainly a good idea, but it also has its drawbacks. While gray water is a lot less harmful to people than the wastewater that leaves your toilet — called black water — it’s still technically sewage. Dishwater contains particulate food matter, which may be rotten. Gray water from your washing machine may contain bleach, which is a hazardous chemical. And bath water may contain fecal matter and dead skin that sloughs off while you bathe. The amounts of these wastes are small enough to prevent gray water from going through the treatment process that black water does, but you still shouldn’t drink it. Your plants, however, will love your bath water.

As a matter of fact, irrigation for lawns and gardens is the only advisable application for using gray water. The United States Environmental Protection Agency says that, in 2007, water used for irrigation constituted 15 percent of total water consumption in the United States . And this was first-run water — the same stuff you drink.


Your plants don’t necessarily need fresh water, and what’s more, some additives in gray water can actually help them grow. Cleaning agents found in laundry detergent — stuff like phosphorus and nitrogen — are actually used in many plant fertilizers sold on the market. Some plants, however, like gray water more than others. Since gray water is alkaline-rich, it’s not suitable for use in watering acid-loving plants like azaleas and rhododendrons.

Be careful watering any plants with gray water without knowing what’s in it first. In addition to nitrogen and phosphate, laundry detergents also contain sodium salts. These salts can build up over time and become toxic to plants, essentially poisoning the soil. To avoid this, avoid using products that contain softening agents — which are generally high levels of salts. You can also cut down on the salt build-up in the soil by alternating your watering applications with gray water and fresh water.

Since the soap you use in the shower is generally less harmful than laundry detergent (it’s mild enough to use on your skin), bath water is the most prized gray water for your plants. But again, there’s the fecal matter. For this reason, some states require that gray water systems remain entirely underground and irrigate plants directly at the roots, using drip irrigation systems. Even gray water proponents who irrigate above ground recommend that the gray water be delivered using the flood method or with drip irrigation. Either way, spraying or misting plants with gray water generally can be a threat to your health. You should also irrigate with gray water on flat ground and avoid allowing it to run off into other yards.

Also because of that pesky fecal matter often found in bath water, gray water proponents advise using gray water to irrigate only your ornamental plants and lawn. It shouldn’t be used for plants that bear fruit or vegetables that you’ll eat — like tomato plants. And under no circumstances should gray water be used for edible root plants, like carrots or potatoes. The roots absorb all of the harmful stuff in gray water.

So now that you know about gray water you may be ready to start using it at your house. But how? Read about some of the methods to get a gray water plan started.

I use dish washing soap diluted with water to spray my flowers and bushes for insects and have good results. My daughter used an anti-bacterial dish washing liquid and killed everything in her garden. What went wrong?

Homemade soap sprays can be a good, easy way to control soft-bodied insects such as aphids and spider mites in the garden. After all, everyone has some dish washing liquid on hand, right? But there are some things to be aware of when applying them.

The soap kills soft-bodied insects by breaking down its protective cuticle or skin. You must make sure that the soapy water comes into contact with the bug for this to happen. You are also spraying your plants so they are affected by the ingredients in the soap spray as well. Depending on what those ingredients are, they can break down the cuticle on your plants as well as the bugs. The best thing to do is to test the spray you have made on a few leaves and wait for 24 hours to see if there is any damage. And make sure the dish washing liquid is pure soap. Nowadays many soaps have extra ingredients in them. Avoid products with degreasers and anti-bacterial agents as these could harm your plants.

Other considerations are not to spray in the full sun, when the temperature is above 90 degrees or the humidity is very high. Make sure your plants are not drought stressed and do not repeat the spray too often. If you’re not sure about conditions, you can always ‘wash’ your plants a couple of hours after by giving them a good rinse with clear water.

One recipe I like to use is to mix 2 teaspoons of dish washing soap with 1 quart of water. Or you can try 1 part rubbing alcohol with 3 parts of water. And remember to spot test!

Re-using at least some of your wastewater on site fits in with permaculture principles, reducing your impact on the environment, as no resources are being used to process it off site. Many areas of Australia have been in drought for years, with garden water availability either limited or curtailed. In these situations, grey water may be the only way to have a garden.

Course Notes

© Karen Sutherland, Edible Eden Design

Why use grey water?

In many households it’s a large and untapped resource, even though its use in gardens is still somewhat new in Australia.

Re-using at least some of your wastewater on site fits in with permaculture principles, reducing your impact on the environment, as no resources are being used to process it off site. Many areas of Australia have been in drought for years, with garden water availability either limited or curtailed. In these situations, grey water may be the only way to have a garden.

Remember that grey water should not be used if there is no need for irrigation normally.

(Note that before considering grey water use in your garden, check with your local council to make sure its use is allowed in your area.)

So can we use this resource to grow produce?

To answer that, we need to understand what grey water is, the basics of safe grey water garden usage and the particular issues that apply to its use on edible plants.

What is grey water?

Grey water is waste water from the laundry and bathroom. The toilet is classified as black water and in Australia kitchen waste water is usually classified as black water. It is advisable not to re-use the water from hand basins and laundry troughs, as it contains many substances not suitable for gardens.

An often over-looked resource is the water saved while warming up the shower, washing fruit and vegetables before eating and vegetable and pasta cooking water. It is possible to save at least 20 litres of this water a day for re-use on pots, herbs and vegetables, and this amount can keep a small vegetable patch alive. The water from rinsing soap from clean dishes is also suitable for use in this way.

Make sure the buckets collecting this are not also used to collect grey water – keep a separate bucket in the house for collecting this water – let’s call it second hand water. Keep a couple of buckets for storage at your back door, and a watering can for giving it to your vegetable patch or pots. Using it at the end of each day avoids it becoming stagnant.

If your water needs are large, you may need to consider using your kitchen washing up water sometimes – if you do so, make sure to avoid any oils or fats in the wash – (wipe them off beforehand with a paper towel) and use the least amount of the simplest, gentlest detergent possible. Do not use washing water from a meal containing animal products and let the water cool before putting it on the garden.

Sit a flexible plastic trough in your sink. After you’ve done your dishes, scoop water out with a plastic jug into 2 buckets, then evenly balanced you can take your waste water out onto the garden. The last bit can be poured out from the flexible trough.

What do we need to know about safe grey water use?

The dangers contained in grey water (for instance it may contain small amounts of faeces, many bacteria and other potentially disease causing organisms), are avoided by following some basic principles:

  1. don’t store grey water for more than 24 hours
  2. don’t allow pets or children to come into contact with it
  3. make sure to water with it underground or under mulch (never above ground)
  4. wash your hands thoroughly after coming into contact with it (try to use gloves)
  5. don’t use grey water if someone in the house has an infectious disease, or you have a new baby in the house
  6. never allow your grey water to run off onto a neighbour’s property or into the stormwater system or into a creek or waterway

What are the issues in using grey water on the produce garden?

For the produce garden, it is not safe to use grey water on the edible parts of plants that are going to be cooked. Grey water is therefore best used on trees, shrubs, large herbs or perennials such as Artichokes, where the edible part of the plant is well away from the soil. However you can safely use second-hand water on plants that are to be eaten raw.

What do we need to know about the quality of grey water and its effect on plant and soil health?

It is advisable to test the pH of your grey water (with a simple aquarium tester kit) and ensure it stays between 6.5 and 7.5. A higher pH will lead to too much Phosporous being available in the soil, and may lead to Iron deficiencies, shown by the interveinal yellowing of leaves, with the veins themselves remaining green. (This can be remedied by applying Sulphate of Iron, available from nurseries, at the recommended rate).

In the laundry, use a low salt, low Phosphorous, low pH liquid detergent. Powders have a pH of more than 8.5 and are usually high in salt. The Lanfax Laboratory website has lists of powder and liquid detergents and their ratings in these regards. At the time of printing, they are still re-working their lists for liquid detergents, but a small list from December 2007 will be at the end of the article in the references, along with the web address for their discussions of grey water and gardens. Make sure you refer to the correct chart for either top-loaders or front loaders, depending upon what you have.

If you must use a powder detergent, only use the grey water on lawns.

In the bathroom, use only liquid soaps, as hard soaps will clog up the soil. For other products, according to a recent study by the ATA (Alternative Technology Association), there is no disadvantage for the garden in using ‘conventional’ bathroom products rather than organic products, or products seen as healthier for the skin. However, using the mildest products, with as little chemicals as possible, is usually best for people’s skin, and is better for the environment generally.

How do we ensure good soil health if using grey water on the garden?

Sandy soils will cope far better than clay soils with grey water, so if you have heavy clay soils, use as little soapy water as possible on it.

Add gypsum each year for the calcium it contributes, which helps the soil deal with salinity. Apply at the recommended rate (usually 1 kg per square metre on garden beds, and 50gm per m2 on lawns). Don’t add lime or dolomite for calcium as they will both raise the pH of the soil and grey water is already probably doing this.

With all soil types it is important to keep up the levels of micro-organisms, nutrients and organic matter – this will help the soil deal with any potential problems from the grey water. So each year add plenty of compost and good quality mulch, such as composted recycled garden waste sold by councils and nurseries.

Never use grey water on potting mix, as it causes the organic matter in it to breakdown and will clog up its drainage capacity.

What are the other issues involved in grey water use in the garden?

The other main issue is to match the amount of grey water generated to the amount of water required by the garden. In some households, the grey water generated will be more than the garden can use, and it may need to be diverted to the sewer when the garden has had adequate water. Conversely, you may have a large and productive garden, with many fruit trees, where you will have to prioritize the water to various trees as they fruit. We will look at the requirements of individual produce plants later.

How do we get the grey water onto the garden?

There are various devices to access the grey water before it reaches the sewer, and divert it to the garden – visit your local hardware, plumbing or irrigation shop and ask for advice. There must always be a way to re-divert the grey water back to the sewer, for instance during winter, when the water is not needed.

Another issue to consider with grey water use is that you may not have the amount of water you need when you want it. Also, soils have become so dry in drought stricken areas, so that water administered to plants can simply run off. Smaller plants can still survive under these circumstances (although not thrive) but established fruit trees with their greater needs (20 or more litres of water a day when fruiting) may drop fruit or not set it at all.

By fitting slotted flexible plastic agricultural pipes (aggie pipes) around your fruit trees, (as many councils do in street tree planting), you can give them a good deep water when they need it, such as when they are setting fruit (at flowering time) and when approaching harvest time. It is amazing how much you can increase the size of your fruit by watering when the fruit is growing. By watering with the pipes, you can get water down deeply into the root zone – difficult to do otherwise.

The pipes should be fitted 30-50cm deep into the ground around the trees, at a distance of about 30 cm from the trunk. A new tree will need 2 pipes, whereas an older established tree may need 4-6 pipes to receive adequate water. Make sure to leave the pipes sticking out of the ground 50mm or so, so that they don’t fill up with mulch too easily. When you are topping up mulch, cover the tops with upturned plastic pots.

Does your home generate enough grey water to use?

In the laundry, top loading washing machines use a lot of water, so their waste water is diluted and quite suitable for garden use. Fill your machine with a 10L bucket, and see how many litres it holds, remembering to add the wash and rinse amounts. Now you can calculate the total grey water generated per day and per week.

The wash water of front loaders is too soapy for most garden use, (except perhaps lawns), but if you can mix it with the rinse water before it goes on the garden, then it would be more suitable, or use the rinse water only. You will need to look at your machine’s specifications to find out its water usage.

In the bathroom, do you have a water-saving shower-head? Regular shower heads usually use 15 litres per minute. Water-saving shower-heads use around 7 litres per minute. So if each person has a 3 minute shower, you are generating either 45 or 21 litres per day per person. Now you can calculate the total grey water output per day and per week.

You have enough grey water, now how do you match its production to your climate, garden size and its particular plants?

Hotter drier climates call for more watering and climates with frequent heavy rain may have no need for additional watering.

Your garden may be small and your grey water production large, so you may be looking for plants that tolerate large amounts of water, or you may have a large garden and a small but steady stream of grey water, that you have to share around your garden, so you need to know which plants simply must have the water and which others will survive on less.

Research thoroughly, plan well and keep a watchful eye on your garden and grey water re-use should be very rewarding.

For further reading:

Ludwig, Art; ‘Create an Oasis with Greywater’

van Dok, Wendy; ‘The water-efficient garden: a guide to sustainable landscaping in Australia’ (The home page for Lanfax Laboratories) (Detailed information on grey water) (Information on grey water and gardens)

From a list from December 2007 on the Lanfaxlab website – some low-salt, low phosphorous, low alkalinity liquid laundry detergents (as the Lanfax Lab website currently has no detergent information)

Enviroclean Liquid Laundry

Earth Choice Laundry Liquid

Earth Choice Wool and Delicates

Ecologic Lavender Laundry Liquid

Bath water is good for plants — just don’t pour it on leaves

Q. I’m trying to conserve water at home and wonder if it’s OK to irrigate my small vegetable garden with bath water.

A. Yes, bath water is fine to use. However, depending on the kinds and amounts of soap and shampoo you use, pouring water directly on foliage could result in leaf burn. Water around the base of your plants only. That’s where it will do the most good, anyway.

Q. I’m very frustrated with a couple of old peach trees I inherited from a previous owner of my property. One has two trunks and one of these trunks is split and falling over a bit. The other has large gobs of sticky sap all over the lower trunk. On top of that, the trees produce very few peaches. Are they worth saving?

A. Probably not. Peach trees, especially those that have been neglected, have a relatively short useful life — about 10 to 15 years. Double-leader trees are inherently weak and tend to split out.

The sap you see is probably the result of peach tree borers feeding directly under the bark. These pests can go undetected for some time. The No. 1 killer of peach trees in Maryland, borers are drawn to trees that have been stressed by drought, low fertility, compact soil, disease problems, etc. You might want to consider removing the trees and selecting a hardier, more pest-resistant fruit variety.

Q. I was given an heirloom tomato plant named Golden Queen by a neighbor who got the seeds in Lancaster County. It produced the prettiest, best-tasting golden orbs. Can I can save and replant seed from these tomatoes even though there are other varieties growing nearby?

A. Yes, by all means save and replant the seed next year. Golden Queen is an open-pollinated cultivar and will come true from seed. However, tomatoes can be cross-pollinated by bees, so there is a slight chance that saved seed will be contaminated with genes from the other varieties.

To ensure absolute purity next year, you should cover your Golden Queen plants with screening or a floating row (from flowering on).


1. Transplant broccoli, cauliflower, cabbage and turnips into open garden beds. Dig in compost before planting and treat young plants with a soluble fertilizer.

2. Water specimen shrubs and trees once a week during dry periods, particularly those that are young or newly planted. Apply water directly from a hose; do not use a sprinkler (whether water-conservation rules are in effect or not).

3. Harvest pumpkins for jack-o’-lanterns. Choose fruit that are full-sized and well-colored. Store in a cool, dry location until Halloween.

Garden tips are provided by the Home and Garden Information Center of the Cooperative Extension Service of the University of Maryland. For additional information on these questions, or if you have questions of your own, call the center’s hot line at 800-342-2507, or visit its Web site at

About Greywater Reuse

Greywater is gently used water from your bathroom sinks, showers, tubs, and washing machines. It is not water that has come into contact with feces, either from the toilet or from washing diapers.

Greywater may contain traces of dirt, food, grease, hair, and certain household cleaning products. While greywater may look “dirty,” it is a safe and even beneficial source of irrigation water in a yard. Keep in mind that if greywater is released into rivers, lakes, or estuaries, its nutrients become pollutants, but to plants, they are valuable fertilizer. Aside from the obvious benefits of saving water (and money on your water bill), reusing your greywater keeps it out of the sewer or septic system, thereby reducing the chance that it will pollute local water bodies. Reusing greywater for irrigation reconnects urban residents and our backyard gardens to the natural water cycle.

The easiest way to use greywater is to pipe it directly outside and use it to water ornamental plants or fruit trees. Greywater can also be used to irrigate vegetable plants as long as it doesn’t touch edible parts of the plants. In any greywater system, it is essential to use “plant friendly” products, those without lots of salt, boron, or chlorine bleach. The build-up of salts and boron in the soil can damage plants. While you’re at it, watch out for your own health: “natural” body products often contain substances toxic to humans (see resource pages below for details).

Our philosophy

We believe that for residential greywater systems simple designs are best. With simple systems you are not able to send greywater into an existing drip irrigation system, but must shape your landscape to allow water to infiltrate into the soil. We recommend simple, low-tech systems that use gravity when ever possible, instead of pumps. We prefer irrigation systems that are designed to avoid clogging, rather than relying on filters and drip irrigation.

We promote greywater reuse as a way to increase the productivity of sustainable backyard ecosystems that produce food, clean water, and shelter wildlife. Such systems recover valuable “waste” products–greywater, household compost, and humanure–and reconnect their human inhabitants to ecological cycles. By modeling “appropriate technologies” for food production, water, and sanitation in the industrialized world, we hope to replace the cultural misconception of “wastewater” with the possibility of a life-generating water culture.

We believe more complex systems are best suited for multi-family, commercial, and industrial scale systems. These systems can treat and reuse large volumes of water, and play a role in water conservation in dense urban housing developments, food processing and manufacturing facilities, schools, universities, and public buildings. Because complex systems rely on pumps and filtration systems, they are often designed by an engineer, are expensive to install and may require regular maintenance.

Basic Greywater Guidelines

Greywater is different from fresh water and requires different guidelines for it to be reused.

  1. Don’t store greywater (more than 24 hours). If you store greywater the nutrients in it will start to break down, creating bad odors.
  2. Minimize contact with greywater. Greywater could potentially contain a pathogen if an infected person’s feces got into the water, so your system should be designed for the water to soak into the ground and not be available for people or animals to drink.
  3. Infiltrate greywater into the ground, don’t allow it to pool up or run off (knowing how well water drains into your soil (or the soil percolation rate of your soil) will help with proper design. Pooling greywater can provide mosquito breeding grounds, as well as a place for human contact with greywater.
  4. Keep your system as simple as possible, avoid pumps, avoid filters that need upkeep. Simple systems last longer, require less maintenance, require less energy and cost less money.
  5. Install a 3-way valve for easy switching between the greywater system and the sewer/septic.
  6. Match the amount of greywater your plants will receive with their irrigation needs.

Types of Simple Systems

From the Washing Machine

Washing machines are typically the easiest source of greywater to reuse because greywater can be diverted without cutting into existing plumbing. Each machine has an internal pump that automatically pumps out the water- you can use that to your advantage to pump the greywater directly to your plants.

Laundry Drum:

“Laundry drum.” Note: Drum should be strapped to the wall for safety.

If you don’t want to invest much money the system (maybe you are a renter), or have a lot of hardscape (concrete/patio) between your house and the area to irrigate, we recommend a laundry drum system.

Wash water is pumped into a “drum,” a large barrel or temporary storage called a surge tank. At the bottom of the drum the water drains out into a hose that is moved around the yard to irrigate. This is the cheapest and easiest system to install, but requires constant moving of the hose for it to be effective at irrigating


Laundry-to-landscape system. Image credit: CleanWaterComponents

If you’re looking for system that gives you flexibility in what plants you’re able irrigate and takes very little maintenance, we recommend the laundry-to-landscape system. This system was invented by Art Ludwig.

This greywater system doesn’t alter the household plumbing: the washing machine drain hose is attached directly to a diverter valve that allows you to switch the flow of greywater between the sewer/septic and the greywater irrigation system. The greywater irrigation system directs water through 1″ tubing with 1/2″ outlets directing water to specific plants. This system is low cost, easy to install, and gives flexibility for irrigation. In most situations this is the number one place to start when choosing a greywater system!

From the Shower:

Showers are a great source of greywater- they usually produce a lot of relatively clean water. To have a simple, effective shower system consider a gravity-based system (no pump). If your yard is located uphill from the house, then you’ll need to have a pumped system.

Branched Drain:

The branched drain system was also invented by Art Ludwig. Greywater in this system flows through standard (1 1/2″ size) drainage pipe, by gravity, always sloping downward at 2% slope, or 1/4 inch drop for every foot traveled horizontally, and the water is divided up into smaller and smaller quantities using a plumbing fitting that splits the flow. The final outlet of each branch flows into a mulched basin, usually to irrigate the root zone of trees or other large perennials. Branched drain systems are time consuming to install, but once finished require very little maintenance and work well for the long term.

From the Sinks:

Kitchen sinks are the source of a fair amount of water, usually very high in organic matter (food, grease, etc.). Kitchen sinks are not allowed under many greywater codes, but are allowed in some states, like Washington, Oregon, Arizona, and Montana. This water will clog many kinds of systems. To avoid clogging, we recommend using a branched drain system with mulch basins, organic matter collects in the woodchips and decomposes. Since bathroom sinks don’t typically generate much water, they can often combine flows with the shower water. Or, the sink water can be drained to a single large plant, or divided to irrigate two or three plants.

Constructed Wetlands:

Constructed wetlands are used to “ecologically dispose” of greywater. If you produce more greywater than you need for irrigation, a constructed wetland can help use up some extra greywater. Wetlands absorb nutrients and filter particles from greywater, enabling it to be stored for longer or sent through a properly designed drip irrigation system (though more filtration and pumping is also required). Greywater is also a good source of irrigation for beautiful, water loving wetland plants. If you live near a natural waterway and don’t have anywhere else to direct greywater, a wetland can safely clean and soak-up greywater, protecting the creek. If you live in an arid climate, or are trying to reduce your fresh water use, we don’t recommend incorporating wetlands into greywater systems as they use up a lot of the water which could otherwise be used for irrigation.

Pumped Systems:

Pumped system. Image credit: Leigh Jerrard

If you can’t use gravity to transport the greywater (your yard is sloped uphill, or it’s flat and the plants are far away) you will need to pump greywater uphill. In a basic pumped system greywater flows into a large (usually 50 gallon) plastic barrel that is either buried or located at ground level. Inside the barrel an effluent pump pushes the water out through irrigation lines (no emitters) to the landscape. Pumps add cost, use electricity, and will break, so avoid this if you can.

Indoor Greywater Use

Sink Positive toilet lid

In most residential situations it is much simpler and more economical to utilize greywater outside, and not create a system that treats the water for indoor use. The exceptions are in houses that have high water use and minimal outdoor irrigation, and for larger buildings like apartments.

There are also very simple ways to reuse greywater inside that are not a “greywater system”. Buckets can catch greywater and clear water, the water wasted while warming up a shower. These buckets can be used to “bucket flush” a toilet, or carried outside. There are also simple designs like Sink Positive, and more complicated systems like the Brac system. Earthships have an interesting system that reuse greywater inside with greenhouse wetlands.

Plants and Greywater

Low tech, simple greywater systems are best suited to specific, large plants. Use them to water trees, bushes, berry patches, shrubs, and large annuals. It’s much more difficult to water lots of small plants that are spread out over a large area. (like a lawn or flower bed)

Additional Greywater Information Pages

  • Greywater friendly products
  • Plants and greywater
  • Laundry-to-landscape greywater system
  • “Greywater-ready” new construction
  • How to conduct a simple percolation test
  • Manufactured greywater systems
  • Commercial scale greywater systems
  • Greywater systems in freezing climates
  • Constructed wetland information
  • Examples of greywater systems
  • Greywater webinars on 11 different topics
  • How to maintain your greywater system (with videos)
  • Greywater resource page

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