Recycling Gray Water for Home Gardens

Thursday, August 16, 2012

In every homestead’s attempt to become more self-sustaining water is a crucial and sometimes elusive commodity. But, using simple rainwater collection systems and reusing gray water from the washing machine on flowers, shrubs and trees, can go a long way to help offset what comes from municipalities.

Southern California is technically a desert. Our annual rainfall hovers around 10 to 15-inches per year. Sometimes we get more, but more times than not it’s less. Sometimes plants in a vegetable garden or flowerbed need more water than is provided through normal rainfall. Or, maybe your area is not known for frequent or steady rainfall throughout the growing season. In those situations most gardeners just turn on an outside faucet to water the garden, drawing on community water supplies, or from a private well.

But, what if you had another way to not only water the garden, berry patch or orchard, but save money as well? With below normal rainfall and droughts in some parts of the country people are looking for other ways to provide gardens with the moisture they need without using what may become a precious supply of fresh water.

One method is to use the wastewater, usually referred to as gray water, produced in the home. But, what is gray water?

Gray water is all the non-toilet wastewater produced in the average household including the water from bathtubs, showers, sinks, washing machines, and dishwashers. Although gray water does not need extensive chemical or biological treatment before it can be used in the garden as irrigation water, it still must be used carefully because it usually contains grease, hair, detergent, cosmetics, dead skin, food particles and small amounts of fecal matter.

How much gray water can be used in the home garden?

First, collect only as much waste water as you will need to meet the water requirements of your garden. The rest should go into your sewer or septic system.

A good rule-of-thumb for deciding how much gray water to use on your garden is that a square foot of well-drained, loamy soil can handle about a half gallon of gray water per week. In other words, if your garden area is 500 square feet, then you can put up to 250 gallons of gray water on your garden each week.

If you can be choosy about the gray water you recycle on your garden, then use shower and bathtub water first, followed in decreasing order of desirability by water from the bathroom sink, utility sink, washing machine, kitchen sink and dishwasher. Water from the kitchen sink and dishwasher is the least desirable because of the larger proportion of grease, food particles and other materials it will contain. If there is no way you can avoid using water from the kitchen sink and dishwasher, try to limit the amount of grease and solid food particles that go down the drain (non-meat food scraps should be composted rather then put down the garbage disposal). NEVER recycle water from a washing machine that has been used to wash baby diapers because it may contain fecal matter.

What about soaps and detergents? Will they harm the soil and plants?

Soaps and detergents are biodegradable, but they can cause problems when gray water is used over a long period. The main problem with most laundry detergents is that they contain sodium salts which, if present in large amounts, can damage the soil structure, can create an alkaline condition, and can also damage plants.

Avoid detergents that advertise “softening power,” because they will have a large amount of sodium-based compounds. The phosphates in detergents can be good for plant growth, but unfortunately, the detergents highest in phosphates usually contain the greatest amount of sodium. If you re-use washing machine water, cut down or eliminate the amount of bleach you use and do not use detergents or additives that contain boron, which is especially toxic to plants.

When doing your household cleaning, use ammonia, or products that contain ammonia, instead of chlorine as the cleaning agent.

What precautions should I take to protect the soil from damage when I use gray water over a long period of time?

A big danger in using gray water is the build-up of sodium in the soil. You can find out if the sodium levels are high by testing the pH of your soil. A pH of 7.5 or above indicates that your soil has become loaded with sodium. You can correct or avoid this problem by spreading gypsum on the soil at a rate of two pounds per 100 square feet about once a month. Rainfall, or alternating gray water applications with fresh water, will help leach sodium and excess salts out of the soil.

The best solution though is to use detergents that are sodium free or low in sodium.

Is there any danger of spreading disease by using gray water in the garden?

Recycled water from the bath, shower, or washing machine can contain organisms causing diseases in humans. However, when gray water is poured onto soil that has an abundance of organic matter, the potentially harmful bacteria and viruses die quickly. If any should survive, it is unlikely that they would be taken up by the roots of garden plants and transferred to the edible portion of food plants. Nevertheless, for safety, you could use gray water primarily to irrigate lawns and ornamental plants, and sparingly on fruits and vegetables.

How should I apply gray water to the soil?

Whether you carry your gray water to the garden by hand in buckets or modify your household plumbing for direct delivery of water to the area where it is needed, a number of guidelines should be followed in applying the water. They include:

If possible, use gray water for your ornamental plants and shrubs and use what fresh water is available for your vegetable garden. If you need to use gray water for irrigating food plants, restrict its application to the soil around plants such as corn, tomatoes, broccoli, or other vegetables of which only the above ground part is eaten. Do not apply gray water to leafy vegetables or root crops.

Apply gray water directly to the soil surface. Do not use an overhead sprinkler, or allow the recycled water to splash off the soil and contact the above-ground portion of the plants. If you have a drip irrigation system, do not use gray water in it since any solid matter it might contain could clog the emitters in the pipe.

Pour gray water on flat garden areas; avoid steep slopes where runoff could be a problem.

Apply wastewater over a broad area; avoid concentrating it on one particular site.

When possible, rotate applications of gray water with fresh water. The fresh water will help leach out any soil contaminants that might be building up.

Apply thick compost mulches to areas where you use gray water. They will speed the natural decomposition of waste residues.

Use gray water on well-established plants only. Seedlings can not withstand the impurities of the waste water.

Do not use gray water, which is alkaline, on acid-loving plants such as rhododendrons and azaleas. Be sure to rotate your use of gray water with fresh water on lawns and fruit trees.

How can I get gray water from the house to the garden?

Gray water can be transported to the garden several ways, the most basic being to bucket the water from the sinks and bathtub into pails and hand carry it to the garden. More sophisticated systems involve siphoning or pumping water from the bathtub or other deep basins (sumps) to the yard through a garden hose, or removing the trap from the bathroom sink drain pipe and putting a five-gallon, or larger, bucket beneath the sink.

When using gray water from the washing machine first drain it into a large bucket (at least 35 gallon) or trashcan fitted with a hose bib so you can attach a hose to carry water to planted areas. Do not attach a hose directly to the washing machine drain. The potential backflow can cause damage to your washer.

For more information on waste water recycling and supplies check out this website


One Response to “Recycling Gray Water for Home Gardens”

  1. coleen says:

    What a great post! We have friends Down Under and just about everyone has their house plumbed to capture their gray water. We live north of Atlanta and, while we are not a desert, we have local water issues. I have thought about reclamation of our gray water; you’ve inspired me to actually DO IT! Thank you.

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