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What you need to know about greywater recycling systems

Joy Persaud / 22 September 2016

What you need to know about installing a greywater recycling system.

Water going down plughole
Greywater recycling systems recycle water to flush toilets and water plants

What is greywater?

Greywater, which makes up 50-80 per cent 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.

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.

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Who uses recycled greywater?

Large establishments and properties, such as hotels and factories, tend to recycle their greywater, 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.

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.

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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-£7,000, 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.


The opinions expressed are those of the author and are not held by Saga unless specifically stated. The material is for general information only and does not constitute investment, tax, legal, medical or other form of advice. You should not rely on this information to make (or refrain from making) any decisions. Always obtain independent, professional advice for your own particular situation.