What is greywater – and how can using it save you money?

Mother and child with washing machine (Getty Images)
Who would have thought your old washing machine water could be so useful? (Getty Images)

Many of us have already heard of collecting rainwater and saving it for another day, but have you heard of greywater recycling? Greywater is the wastewater collected from baths, showers, washing machines, dishwashers and sinks, but instead of relying on rainfall, greywater is in plentiful supply on a daily basis.

Greywater typically makes up between 50-80% of a household’s wastewater, according to The Green Age. It’s called ‘grey’ because it usually contains residue dirt, grease, hair and any cleaning products you may have used. Although it’s not safe for drinking, of course, and may look dirty, it is perfectly safe to reuse for things like flushing the toilet, cleaning your home or watering the garden.

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Greywater is great for people and planet. Not only is it an easy way to save money, but if it’s recycled properly, it can save approximately 70 litres of water every day – nearly half of the estimated 142 litres of water we each use day, according to the Energy Saving Trust.

Where do you find greywater?

From our washing machines to kitchen sinks and bathtubs, greywater can be easily sourced from anywhere water is found in our homes.

Washing machines use a lot of water. According to The Energy Saving Trust, the average household uses their washing machine a whopping 274 times a year. Each cycle uses 10 litres of water for every kilogram of clothes it cleans on a standard 40-degree wash.

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Recycling washing machine water is an easy way to immediately reduce water consumption and cut back costs on your water bill. But how on earth do you get that water out?

To do this, you’ll need to run the washing machine’s discharge hose into a container. Simply cut a hole to fit the hose in a large container lid and put the hose through the top. Water from your washing machine will flow into the container after each load of laundry and you can empty and refill it after each use.

Washing machines are the number one household appliance when it comes to water consumption. The average household uses their washing machine nearly 300 times each year. (Getty Images)
Washing machines are the number one household appliance when it comes to water consumption. The average household uses their washing machine nearly 300 times each year. (Getty Images)

You can also call a professional plumber and have them set up a new drainage system directly to your toilet. “One of the easiest ways to reuse grey water from the washing machine is to divert it towards your home’s toilet,” says Jeyree Everly of Enviro Design Products. “In areas where water is scarce or expensive, there is no need to use fresh drinking water to flush the toilet – and no treatment is necessary.”

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Greywater can also be collected from the shower or bath. And since it contains fewer chemicals than greywater collected from the washing machine or kitchen sink, it's easier to reuse your old shower water without having to invest in sophisticated treatment systems beforehand.

Woman in shower smiling (Getty Images)
Greywater can be collected from the shower or bath and reused in multiple ways. (Getty Images)

“Diverting shower greywater directly to the garden only requires a storage and filter system that deposits the water underground,” says Everly. “It’s better to discharge greywater underground and irrigate plants directly at the roots rather than on the surface because pooling greywater can become a breeding ground for bacteria and insects.”

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And when it comes to reusing kitchen sink water, it’s important to ensure it doesn’t contain large amounts of food waste.

“If the level of organic waste is too high, the water will require significant treatment to become usable grey water,” warns Everly. “With the highest concentrations of organic matter, kitchen sink greywater is ideal for flushing toilets and carrying sewage away from the property. At low concentrations, a simple water purification system is enough for recycling grey water effectively.”

How do I use greywater?

It’s important to ensure you don't store untreated greywater for more than 24 hours – if you can't use it, don't keep it. Since greywater has already been used and is contaminated with germs or products, storing it requires treatment, or it will soon start to smell.

Using greywater is especially useful during a drought, or a hosepipe ban, which some water providers across the UK have confirmed will continue into the new year.

Read more: UK hosepipe ban: Irrigation systems, watering cans and other ways to water your plants

“Reusing your greywater from baths, kitchen sinks and even washing machines is a great short-term solution to hydrating your garden sustainably – perfect for cutting back on your water bill without neglecting your garden,” says Matt Jordan, a gardening expert at The Greenhouse People.

With the hosepipe ban still in effect, using greywater is a great short-term solution to hydrating your garden sustainably. (Getty Images)
With the hosepipe ban still in effect, using greywater is a great short-term solution to hydrating your garden sustainably. (Getty Images)

“Soil and potting composts are very efficient at filtering contaminants, so it is generally safe to use greywater on your plants. Just be sure to use the leftover water within 24 hours to avoid bacteria building up.”

“Best practice is to use water that hasn’t been exposed to harsh chemicals or contains too much salt content. So, it’s best to avoid using left-over water from your dishwasher, or you may start to see salt residue developing on your plants,” Jordan explains.

And when it comes to flushing toilets, the simple task uses more water than you might think. According to Waterwise, flushing toilets uses approximately one-third of household water.

Greywater can be used to fulfill this purpose and save valuable water by simply pumping it into the toilet bowl after use. Just be sure not to put greywater into the toilet tank, as it could not only cause the flushing mechanism to malfunction but could also be back-siphoned into the freshwater supply if water pressure decreases suddenly, warns Renewable Energy website REUK.