14th February 2025
Grey water is water that has been used for washing hands, bathing, washing clothes, washing vegetables etc. Grey water systems that collect and treat grey water, often combining it with collected rainwater, can be plumbed in to flush toilets but these can be expensive, especially when retrofitted.
In summer months, we may already practice grey water harvesting – collecting water from showers and washing machines to water the garden. Ideally such water should not be stored from more than a day because pathogens from what we have washed may multiply especially when the water is warm.
The Centre for Alternative Technologies has this advice about washing machine water – “If you wish to irrigate with water from a washing machine then use a low-sodium detergent, because sodium damages plants and degrades soil (liquid detergents usually contain less salt than powders). Avoid phosphorus as well, because this causes algal blooms if it collects in ponds or rivers. Otherwise, the water has only very small and well diluted quantities of pathogens or grease and therefore these should not be of concern.” https://cat.org.uk/info-resources/free-information-service/water-and-sanitation/rain-and-grey-water/
And the RHS says – “Plants can be watered with shower, bath, kitchen and washing machine water (from rinse cycles), collectively referred to as ‘grey’ water. It varies in quality and may contain contaminants such as soap and detergent. Fortunately, soil and potting composts are effective at filtering them out, and the residues can sometimes act as a mild fertiliser. To minimise bacterial growth, grey water should be saved for only 24 hours, unless filtered through a reed bed or professionally designed system. It is best applied by watering can; grease and fibres can clog irrigation systems.” https://www.rhs.org.uk/science/gardening-in-a-changing-world/water-use-in-gardens/using-grey-water
In our home, we collect hand wash water and use it to flush the toilet when ‘yellow’ and use the toilet flush when ‘brown’.
The Green Tau 