Hosepipe restrictions are hitting England and Wales, and the hot weather is leaving many gardens parched and wilting.
The good news? You don't need a hose to save your plants – the solution is already sitting in your bath, shower and sink: grey water.
What is grey water and can you use it in the garden?
According to the RHS, grey water includes water from showers, baths, kitchens and washing-machine rinse cycles. It may contain soap, detergent and other contaminants but there should be “no problem with small-scale, short-term use of grey water to tide plants over in summer drought”.
When the water butt is bone dry and the hosepipe is off limits, yesterday’s shower water may be enough to stop your borders throwing in the towel.
Can you use grey water during a hosepipe ban?
Whether you can use leftover shower and bath water during a hosepipe ban depends entirely on your water company. Water UK advises checking your local restrictions, as exemptions vary between suppliers.
Thames Water, for example, explicitly allows grey water and rainwater collected in a butt for most restricted activities. It also permits bucket-and-watering-can application of mains water for those same tasks. But swimming pools and ornamental fountains have separate rules, and other suppliers may differ entirely.
Check your water company's legal notice before you start stockpiling shower water. A quick online search will tell you what's permitted in your area.
Which types of household water can you use?
Bath, shower and washing-machine water
Water from showers, baths and washing-machine rinse cycles can all be reused, provided it doesn’t contain bleach, disinfectant, dishwasher salt or harsh cleaning products. According to Severn Trent Water, “soil and potting composts are effective at filtering them out”, while detergent residues “can sometimes act as a mild fertiliser”.
Kitchen water
Water from kitchen sinks can also be reused, provided it doesn’t contain bleach, disinfectant, dishwasher salt or harsh cleaning products. Water used to rinse fruit and vegetables can go on garden, house or container plants.
Avoid using greasy washing-up water or putting it through narrow irrigation pipes, as grease and food scraps may cause blockages.
Fish-tank water
Fish-tank water is useful too, although it isn’t technically grey water. Severn Trent says: “The nutrients left in the water save the need to add extra fertiliser.”
Water to avoid
Don’t use water containing bleach, disinfectant or strong cleaning products. Dishwasher water and softened tap water are also less suitable because they contain salts that may damage soil structure, particularly in clay soils.
The RHS says short-term use of softened water is unlikely to cause serious damage and may be worth considering in an emergency. Even so, rainwater, ordinary mains water or lower-detergent grey water are better choices where available.
Which plants can you water with grey water?
The RHS advises using grey water on “ornamental plants, rather than edible crops”. It adds that, where grey water’s used on food crops, gardeners should “limit it to crops that will be cooked”. Don’t use it on salads, herbs or anything else that’ll be eaten raw.
RHS experiments found that using grey water for several weeks didn’t significantly affect the function of the ornamental plants tested. However, “after 6 weeks some plants” were “beginning to show signs of salt stress”. These plants benefited from being rinsed through with tap water.
Don’t treat six weeks as a guaranteed safe window. Plant sensitivity, detergent levels, soil and watering frequency will all vary. Alternate grey water with rainwater or mains water where possible to reduce the build-up of mineral salts.
How to safely reuse leftover household water
Don’t leave untreated grey water sitting around. The RHS advises using it within 24 hours unless it has been treated through a properly designed filtration system. Stored grey water can begin to smell and may allow microorganisms to multiply.
Apply grey water directly to the soil around established plants rather than spraying it over the leaves. Avoid putting water containing fibres through narrow irrigation pipes, as they may become blocked.
Use grey water as a temporary backup during dry spells for well-established plants. Rotate it with tap or rainwater, and stop if your plants look unhappy.
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