Grey water is water collected after doing activities such as washing laundry, washing yourself and washing the dishes. Sewerage is not grey water - it is usually called 'black water'. Grey water can be collected in a number of ways: you can collect it manually by using a sink insert when washing dishes or putting buckets in the shower when you're showing for example; or you can install grey water recycling systems which will collect the water and store it. Storage tanks used to store water collected via the latter method, can have pumps attached to them to assist when watering the garden or they can just have hoses attached and can be gravity fed if your property is on a slope.
Grey water can be used in the garden to reduce the amount of water you take out of local dams and of course, to reduce your water bill but there are a number of things you need to consider before doing so and the use of grey water on gardens is very controversial. Many governments and councils also have policies that cover grey water use so if you want to use grey water in your garden, you need to check with these authorities to ensure that you're allowed to do so.
Laundry Water and Dish Water
Many laundry and dish washing detergents (whether powder or liquid) contain high levels of phosphate, salts and other chemicals that can be harmful to your garden and to local water ways if they are washed off your property or leached into the water table. In particular, EDTA and some other chemicals can increase the amount of heavy metals uptaken by plants and many chemicals used in these products can persist in the soil for a long time and are thus damaging in the long term and are difficult to remove once deposited. Thus if you want to use water collected from your washing machine, water used to hand wash clothes, water from a dishwasher or water from hand washing dishes, you'll need to find a source of ‘garden friendly' detergents. You won't be able to use bleach either. You should pay particular attention to any detergents used in dish washers, as many of these are highly alkaline and this can have an adverse effect on your garden.
Water used in the rinse cycle of a washing machine or dish washer is much cleaner and safer to use than the water used in the wash cycle. For this reason you may wish to only recycle water from the rinse cycle of such appliances. Water used to wash clothes is much cleaner than water used to wash dishes as dish water is heavily polluted with food particles, oil and other wastes. Many areas discourage the use of dish water in the garden as these food contaminants promote the growth of harmful microorganisms and thus dish water is likely to have more pathogens in it than grey water obtained from other sources. These food contaminants can also clog grey water systems. More than that, some of these contaminants may harm your plants and they can attract pest insects or even rodents.
Never recycle the water used to wash nappies.
Shower and Bath Water
Shampoos, body wash, soaps, cleansers, conditioners, shaving cream... if you want to recycle shower or bath water you need to make sure that every product you use in the shower and/or bath is garden safe. You can however manually collect the water wasted when you're waiting for it to get to the right temperature etc.
If someone in the household has a gastrointestinal illness, it is best to avoid using grey water from the bathroom until the person recovers.
General Tap Water
If you want to collect tap water that you use to wash your hands etc. again make sure that the soap you use is garden friendly. Again if anyone has a gastrointestinal illness, it's best not to use general tap water as grey water until the person has recovered.
Special attention should be paid to any product entering grey water that contains boron. Even small increases in soil boron levels can cause toxicity in plants so ensure that your detergent and other products do not contain boron.
Regardless of the source of your grey water, it should be treated as if it contains potentially harmful pathogens - bacteria/fungal spores/viruses from the food residue on your plates, the clothes you wear, your hands etc. For this reason, you should carefully consider whether you want to use grey water to water any plants you plan to eat as there is the possibility that the plant will harbour these pathogens, that they will multiply and thus that eating the plant material could make you very sick. Many gardeners have been pouring grey water over their edible crops for years and haven't had problems but others consider it too great a risk and indeed it is not allowed in some areas. Either way, if the food you grow is going to feed anyone not in your own family, children, elderly people or anyone with digestive problems or a compromised immune system, you should not use grey water on edible crops. You also may not wish to use grey water on edible crops or even on ornamentals if you have pets. In particular, you should not use grey water to irrigate any plant that may be eaten raw.
You should also be wary of using freshly collected grey water. Even if you use garden friendly detergents, there will be ingredients in the water that remain active for a period of time after use and these may cause harm to your plants. After all, one of the roles performed by detergents is to break open cells so if applied to your plants in the quantities typically found in grey water, they may damage your plant cells. If you store the water for a period of time (no longer than 24 hours) microorganisms will break down residual active ingredients from eco-friendly products as they are by design made to bio-degrade quickly and the water will thus be safer to use on your plants. You should not however store it for too long, otherwise harmful pathogens will multiply and you could get sick when you water with it. Children should not be allowed to water with grey water that has been stored for any length of time as they are more susceptible to any pathogens that may multiply. Immune-compromised individuals and elderly people may also wish to avoid using grey water that has been stored for the same reason. If you want to store grey water for more than 24 hours, it will need to be treated.
It is also best to use grey water directly on the soil only, rather than wetting above ground plant parts with it. This allows soil microorganisms to further break down the detergent residues. If you have a dripper system that is designed to use grey water, that is a good way to apply it. Don't put grey water through hoses or sprinklers etc. unless they have been designed to use grey water. It's also a good idea to avoid spraying grey water as it can allow pathogens to become airborne and again they can make you sick. If you want to spray grey water, it should be treated first. Sub-soil, sub-surface and covered surface irrigation systems are available to enable you easily irrigate your garden with grey water without producing aerosols. If you don't have such a system, it is best to apply grey water using a bucket or something similar.
The risk of contracting a disease from properly used grey water is considered low, however you should always wash your hands well after watering your garden if you use grey water. Likewise, if you touch plants (including lawns) or garden tools that have been watered or have otherwise come into contact with grey water, you should also wash your hands. If you use any in-ground water supplies for drinking or bathing, such as a damn or an in-ground water tank, you should take special care to ensure that grey water does not contaminate these.
The health of your soil can be maintained by choosing garden friendly cleaning products but you can further maintain soil health by alternating your use of grey water with water from other sources such as rainwater from a tank or town water.
Many areas have laws in place that prevent people from creating unsanitary conditions and from polluting the environment. Other laws also prevent people from putting anything into drinking water supplies that is detrimental to the quality of the water. Therefore, you must make sure that no grey water leaves your property and that it doesn't form puddles or pools on your property where it may fester and create unsanitary conditions.
- Immuno-compromised people, elderly people and children should avoid using grey water
- Grey water should not be used on any plants that are eaten raw or plants that will be eaten by anyone outside your family
- Collect grey water from the cleanest sources - dish washing is not a good source of grey water
- Use garden friendly detergents and other products that don't contain boron, sodium salts or other harmful chemicals
- Don't store grey water for more than 24 hours unless it is treated
- Don't spray grey water
- Don't let grey water leave your property or enter underground drinking water supplies
- Don't let grey water form puddles on your property
- Grey water should not be used if anyone in the household has a gastrointestinal illness