Around 30% of the water we use in the home is quite literally flushed down the toilet, 33% is used for washing and bathing, while just 4% is used for drinking — although 100% is of drinking quality (WaterWise, 2017). Up to 12% of that water is used outdoors for car washing and watering the garden.

We have a finite amount of water available. Clearly, at some point, something will have to give, so water conservation should really be at the top of your list. WaterWise, the UK agency charged with monitoring such issues, suggest that 55% of the water we use could come from rainwater harvesting. So what domestic water recycling options are available?

Recycling and rainwater harvesting: What are the options?

Rainwater harvesting and greywater recycling both generate water for use in the home. Recycled greywater and filtered rainwater are similar in that neither is toxic (black water), neither is drinkable, and they do the same job — they can be used for garden irrigation, washing the car, flushing toilets and for laundry.

  • Greywater recycling can deal with up to 60% – or around 140,000 litres – of the water entering the house (assuming a family of four).
  • A rainwater harvesting system can provide 56,000-130,000 litres, depending on rainfall levels and roof size.

What both systems do is make more water available to the home. Hosepipe bans and consumption reduction for Building Regulations can be dealt with, with little inconvenience.

A borehole is another option in reducing demand on the water grid. They’re a well-established technology, but the practicality, depth and cost will be entirely dependent on the location. A borehole, capped with a manhole and a suitable pump installed, will cost upwards of £2,500 but could set you back over £20,000.

Greywater Recycling

A whole-house system which recycles and filters greywater from taps, baths, washing machines, and provides water for external use, flushing toilets and laundry, etc., can cost in the region of £5,000 to £7,000 installed.

Rainwater Harvesting

In basic terms, rainwater harvesting comes in two forms:

  • systems that enable the collection of rainwater, which is then filtered, disinfected, stored and made available for use in the garden and house;
  • or water butts.

The former requires a storage tank, which is typically buried underground, but can also be installed above.

installing a rainwater harvesting tank

‘Shallow dig’ tanks, such as F-Line Flat Tank available at Rainwater Harvesting, helps save on excavation, spoil and associated labour costs.

Which Type of Rainwater Harvesting Tank Should You Choose?

This depends on what you are willing to spend and what you would like to use the water for:

Water Butts

Three or four water butts (situated at the foot of drainpipes on the home or outbuildings) can be used for small-scale garden watering (you need around 24 litres of water for every m² every week). With a pump fitted they can even provide water for washing the car, as well as watering the garden.

A 200 litre water butt can be picked up for as little as £25. A couple of hundred pounds will provide all the water butts needed to meet the whole of a home’s external usage, and that can be up to 40% of the house’s total demand.

Above-Ground Water Tanks

Above-ground water tanks can be used for toilets, garden watering and anything where the water does not need to be filtered. They can be put on roofs if they gravity-feed the water to points of use without the need for a pump. However, that requires roof space and supporting steels to bear the extra weight.

Mounted on the ground, with a pump fitted tends to be easier and cost will be between £1,000 and £3,000, depending on size. Installation cost is relatively low but will vary with access to the tank’s preferred position.

Underground Tanks

Underground tanks are the most expensive to buy, install and run (as they use a pump), but offer the greatest savings and the most uses. These can be installed anywhere, but placement under driveways is popular and can help mitigate flooding issues where hard surfaces are used.

They are preferable if you are concerned about the risk of legionella — an underground tank cannot be disturbed and stores water at 11°C which removes the risk. Being below ground also stops them from freezing.

Costs vary with the size and the installation. A good quality system with capacity to store 5,000 litres will cost around £2,000 to £2,500. Installation costs can be high due to the need to excavate a hole large enough to accommodate the tank; add to that the cost of installing the pipe work and the price could easily double.

Slim-line Solution

Mike and Jane Fry self built their award-winning 72m² home on their former garden in Somerset. Keen to be as sustainable as possible, and to keep utility bills to a minimum during their retirement, the property is highly insulated and features solar thermal panels. There’s also a sedum roof, which reduces rain surface runoff, along with a rainwater harvesting system.

A low-cost sustainable home

“The rainwater harvesting is unlikely to pay for itself, but we included it for the feel-good factor,” says Mike.

The couple opted for Halsted’s Slim-Line Rainwater Harvesting System; a good solution for their tight plot. The narrow, above-ground tanks are now hidden on the house’s rear façade.

“Installation was a relatively straightforward DIY task, too. This system suits urban homes and smaller households, but you’d likely need a bigger system otherwise,” advises Mike.

Running Costs

Greywater and rainwater harvesting systems both use a small amount of electricity. In all cases there is a running cost to consider and a maintenance requirement. Running costs tend to be £30-£50 per year, but will depend on the system. While some of the gravity-fed systems are notionally running cost-free, there is still a need to change filters.

Greywater recycling requires a greater degree of filtration than rainwater and so maintenance costs can be higher too. It’s also worth noting that all systems include mechanical and electrical components, so there’s always the slight chance that they could be subject to breakdown.

Retrofit Water Recycling Solutions

Whole-house greywater recycling can be difficult in a retrofit as it will mean significant changes to the existing plumbing. Equally, digging a large hole for a rainwater harvesting tank may not be a good idea in an established garden; that said, an above-ground tank solves this.

There are also rainwater harvesting systems specifically designed for retrofit, like Astro Turf systems, which tend to be more compact and cheaper.

Maintenance

We ask Lisa Farnsworth, of rainwater harvesting manufacturer Stormsaver, what to consider:

“There are typically two stages of filtration with rainwater harvesting, and the filters will require cleaning/rinsing through every three to six months — sometimes just once a year, depending on the system. Most tanks are designed to overflow a couple of times a year too, meaning any scrum or debris at the top is removed. The main issue, however, is leaves. Clearing gutters regularly is important, and systems installed on homes in close proximity to trees could require more maintenance.

“Another consideration is the pump: ask your supplier/manufacturer how the water is pumped, and what the voltage is? This can have an impact on running costs and energy consumption. Our Monsoon system uses a 90W pump, compared to other systems which use a 800W submersible pump. This can reduce energy consumption by over 75%. It can be connected to a small solar panel too. There are limitations though; such pumps aren’t always possible with longer pipe runs (for example, if the tank is located at the end of a long garden).

“Also enquire whether the incoming supply is AC or DC. With a DC supply, the pump can be connected to a battery back-up so that if the power fails, the homeowner will always have a water supply for toilet flushing.”

What Else Should You Consider When Recycling Water?

The first option could be to use less water in the first place. Providing hot water to house typically accounts for 25% of the energy bill. If the requirement is to make more water available to the house, then greywater or rainwater harvesting will both do that. Such systems come into their own in new builds where either system can be designed-in from the outset, making them cheaper and easier to deal with. In terms of capital cost, running cost and effectiveness, there is little to choose between them; both have cheap and more expensive options.

The size, type and location of the property will be factors too, but ultimately the decision will be down to the homeowner’s preference.

It’s also important to note that cutting down water in the first instance can make an impact. The following are much cheaper than installing water recycling but will reduce your water usage considerably, so you might want to consider them first:

  • aerated taps
  • flow regulators
  • ultra-low flush toilets

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