12 pointers for using grey water in your garden

The water from your laundry and bathroom – also called “grey water” – is a great additional resource for gardens, especially when rainwater is scarce. Here are 12 tips for using grey water safely in your garden.

The average household produces between 200 and 800 litres (around 45–175 gallons) of grey water per week from sinks, bath tubs, showers and washing machines. If your system is set up efficiently and you implement the precautions listed below, it should take little effort to put this water to good use in your garden.

1. Check the legal requirements with your local municipality. Most authorities insist that water must be kept within the boundary of where it was produced. Therefore, it is not allowed to go onto a neighbour's land or into storm drains.
2. It's best to apply grey water to your garden using a subsurface irrigation system. If you pour it directly onto the surface of your garden, it can become a health hazard for humans and animals.
3. Use only the rinsing water from a washing machine load to ensure that you do not introduce concentrated detergents into the garden.
4. Don't use any water from a washing machine load of diapers as it may contain fecal matter that carries pathogens.
5. Use grey water only when it has cooled, as hot water can damage plant roots.
6. Where grey water is continually applied, treat the soil with gypsum to help break down salts such as sodium (present in some detergents and washing powders), which could eventually kill plant life. Diluting with rain or water will also help.
7. The fats from the soap in grey water can make the soil water-repellent. If this occurs, treat the soil with a wetting agent every six months or so.
8. When it's raining, don't use grey water – let it run down the drain.
9. Don't use grey water to water vegetables or children's play areas.
10. Check the pH of your soil. Grey water tends to increase its alkalinity, which can lead to iron deficiencies in plants. (Symptoms include new yellow leaves and green veins.) If necessary, remedy the problem by adding sulfate or iron to the soil.
11. Don't use grey water on the garden if it is likely to contain phosphorus (present in some detergents). Some plants struggle with excess phosphorus, as it is toxic to them. Too much phosphorus in other plants can cause iron deficiencies.
12. Use less fertilizer.

Don't let your grey water go to waste – instead, put it to productive use in the garden and reduce your overall household water consumption.