What you need to know about greywater recycling systems

What is greywater?

Greywater, which makes up 50-80% of a household’s water, comes from baths, showers, sinks, dishwashers and washing machines. It’s water that doesn’t come into contact with faeces, which means it’s possible to treat and reuse it around the home for flushing the toilet, washing laundry and watering the garden. It should never be used for drinking water, cooking, bathing or washing the dishes.

"Blackwater" is the term used for water used when flushing the toilet and it's dangerous to reuse.

How much water can be saved?

On average, greywater recycling can save approximately 70 litres of potable (drinking quality) water per person, per day. Cost savings depend on usage but if you have a water meter, you’ll use less and possibly recoup savings in the long term.

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Is greywater safe?

Waterborne diseases cause some of the world’s biggest health problems, so it is essential that greywater is treated. Washing underwear, raw meat and wounds with water that subsequently ends up in a tank, can lead to an increase in harmful bacteria. After just a few days, this can lead to a stench that will need chemical intervention or filtering. Remember that even when treated, greywater won’t be safe to drink, but can be used for flushing toilets and watering plants.

What can untreated greywater be used for?

Untreated greywater can be siphoned off using gravity to irrigate ornamental plants and trees. It shouldn’t be used on edible parts of fruit or crops, as there is a risk that harmful pathogens will be absorbed by the plant – and then eaten by humans. Untreated greywater needs to be used swiftly to minimise the growth of bacteria.

Find out how your garden can help reduce the risk of flash flooding after long periods of drought

Who uses recycled greywater?

Large establishments and properties, such as hotels and factories, tend to be more likely to recycle their greywater than residential homes, simply because the process can be expensive to carry out and maintain. The energy costs involved in pumping water into a storage tank, treating it and then pumping it out can mean a recycling system is not particularly environmentally friendly or cheap to run on a small scale, although there are cheap and practical ways to collect your grey water (see below).

With increasing interest in eco-friendly living we're likely to see more and more residential homes recycle greywater, and advances in the technology happening in Europe and the USA is inevitably going to make it more cost-effective eventually.

How can you clean greywater naturally?

Biological filtration systems send the water through various layers of sand and soil to first remove larger particles and then smaller ones. Organisms in the soil feed and reproduce in the soil, purifying it.

What about chemical disinfection?

Some people disinfect their greywater with chlorine, which is relatively cheap and easy to obtain. Chlorine tablets or liquid, as used in swimming pools, is easiest to obtain. Also, it will evaporate from the water once the process is complete. The disadvantage of using chlorine is that it can kill or harm plants if used excessively and can have a negative impact on soil quality. 

If you want to use greywater in toilet flushing, it must be disinfected to avoid splashes contaminating surroundings. Any chlorine-treated greywater needs to be stored overnight to allow the gas to dissipate. Some companies sell disinfectant that turns the water pink, so you can be sure it has been adequately decontaminated.

Find out how to make your home more eco-friendly

How much cleaning is involved?

Simple filters, which are usually made of ceramic or charcoal, are usually used to remove organic matter and to prevent large particles from getting into a storage tank. You can clean these by soaking them in a vinegar solution or, for higher-spec systems, buy new ones and replace them regularly.

How much does a complete greywater system cost?

As the prices are currently high (around £4,000-£8,000, which includes installation), whole-house greywater systems tend not to be geared towards typical domestic homes. Simple systems, however, where bath and shower water is stored and used to flush the toilet, start at around £1,000. It can take up to seven years for a system to pay for itself, though this is expected to fall as more people buy them and new-build properties include them. Employ a qualified greywater installer to fit your system, as waste pipes must be correctly aligned.

Do systems need servicing?

More complex systems will require a specialist to pay an annual maintenance visit to check that high-tech filter membranes are clear – this could cost around £150-£200 a year. Simple systems cost around £50 to service.

What are the disadvantages?

If you decide to move home, prospective buyers may not wish to commit to the expense of keeping and servicing a greywater system. And, you may have to pay for a new system if you want to keep recycling greywater in your next property.

Easy ways to save greywater (without installing a greywater system)

Not letting your water trickle down the plughole when the tap is running is a good habit to get into. If you're waiting for the water to heat up to wash or do the dishes keep a jug or bottle to hand and let the water run into it while it warms up. This can be used to refill the toilet cistern after flushing or to water plants around the house.

Keep your washing up bowl water and, when cool, pour it around the base of thirsty shrubs or trees. Use it as quickly as possible and avoid it touching edible plants such as herbs or vegetables.

Empty your bathwater with either one of the old fashioned ways – a bucket or makeshift hosepipe siphon, or by using a pump (prices start at around £70). Use in the garden or keep to hand for refilling the toilet cistern.

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