House Design

Rainwater harvesting: how to conserve a precious resource for use at home

Raintwater harvesting helps you be eco-friendly and get free water for your home and backyard

Rainwater harvesting - garden leaf
(Image credit: Unsplash/Peter Lloyd)

Domestic rainwater harvesting is a growing trend – although it’s a long established water conservation measure. By collecting and re-using rainwater in your yard or inside your home as well, you can reduce your reliance on municipal or mains water, help conserve energy as well as water, and enjoy other benefits, too.

The average American family uses over 300 gallons of water per day at home, according to the US Environmental Protection Agency (EPA). In the UK, meanwhile, the average household uses around 330 liters a day – that’s 140 liters per person per day, says the Environment Agency.

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’If we do not increase water supply, reduce demand and cut down on wastage, many areas will face significant water deficits by 2050,’ said Emma Howard Boyd, chair of the Environment Agency in the State of the Environment: water resources research and analysis published in 2018 and updated in 2020.

The extreme weather caused by climate change plus population growth makes water shortages a pressing concern, so harvesting rainwater is an eco-conscious move. But it can additionally reduce the run-off of stormwater which benefits the environment, too. Garden plants will also appreciate non-treated water.

Find out more about rainwater harvesting and decide if a system is right for your home. 

What is rainwater harvesting?

Rainwater harvesting

(Image credit: Markus Spiske/Unsplash)

Rainwater harvesting is the process by which rainwater is collected and stored for re-use later on. The water could simply be used for irrigating the backyard. But it’s also possible to use it indoors for processes such as flushing the toilet and doing the laundry, or – in the most sophisticated systems – used all around the house including for drinking.

There are many advantages to rainwater harvesting. It’s a way of reducing reliance on municipal or mains water beyond what you can do by fitting faucets, showers, toilets and appliances that use less water. 

As well as responding to climate change by conserving water, it also has the benefit of reducing the stormwater run-off that can erode the banks of streams, spread pollutants and could cause local flooding.

Although whichever rainwater harvesting system you choose will have associated costs, the rain comes free, resulting in less annual expenditure for your household as well as a more eco-friendly home.

When it comes to keeping the garden in great shape, rainwater suits most plants, and means you don’t have to use drinking quality water where it’s not required. 

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How much water can be collected?

When you’re planning a rainwater harvesting system, you’ll want to first find out what the rainfall levels are like where you live and therefore how much you might be able to collect.

Check the figures for your region via Current Results, which covers both the states of the US and the areas of the UK. After that, use the ‘flat area’ of the roof (this is usually the same as the footprint of the house below), multiply by the annual rainfall and deduct 20 per cent for evaporation and overflow (multiply your result by 0.8 to make this deduction). The answer is the amount of potentially collectable rainwater each year.

What are the rainwater harvesting system options?

Rainwater harvesting

(Image credit: Jura Greyling/Unsplash)

You should consider the water you use both outside and inside your home when you’re planning to start rainwater harvesting. 

‘Nationally, outdoor water use accounts for 30 per cent of household use yet can be much higher in drier parts of the country and in more water-intensive landscapes,’ says the EPA. ‘For example, the arid west has some of the highest per capita residential water use because of landscape irrigation.’

If you like the idea of irrigating the garden and washing the car without using municipal water, you can start rainwater harvesting at low cost. Gutters and downspouts emptying into a rain barrel or more than one will get a supply started. Since these barrels generally store from around 50 to 100 gallons (or in the UK have 200 to 300 liter capacities), this might not meet all your needs. Potential overflow and therefore waste could be another downside. On a positive note, they take up little space so are suitable for backyards of most sizes, making rainwater harvesting available to many.

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‘Direct and indirect sunlight will act as a catalyst for algae growth in the cistern, so exposure to sunlight should be limited where possible,’ says the EPA in its report Rainwater harvesting: conservation, credit, codes, and cost literature review and case studies.

Like the idea of collecting more water? You can size up to a larger tank in what’s called a ‘dry’ system. The storage tank is still located beside the house, as with a rain barrel, but the storage capacity is much larger and it can cope with the volume of precipitation caused by storms. 

More sophisticated is a ‘wet’ system. In one of these downspouts from gutters around the house are connected to piping through which the water travels to a large tank. A system like this allows the whole collection surface to be used. Another plus point is that the tank can be located away from the house. It can be positioned above ground, but there’s also the potential to hide it underground. Tanks sited below ground also keep the stored water at a relatively constant temperature, inhibiting the growth of bacteria. 

Use rainwater indoors

rainwater harvesting - laundry room

(Image credit: Ashton House Design )

Inside a home, fixtures such as toilets and clothes washers don’t require potable water, that is water that’s suitable for drinking. For these needs harvested rainwater is an alternative, and using it instead conserves drinking water for situations when its use is essential. 

But it’s also feasible to use harvested rainwater to fulfill potable water needs, provided it is both filtered and disinfected. This therefore requires a more sophisticated whole-house harvesting set-up.

 As well as the storage tank and pipes, a whole-house system includes pumps, filters, connectors and a control system. In the UK, mains water back-up is featured in the system, while in the US they ‘are often supported by municipal or private well water supplies as a back-up water source’, according to the EPA.

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Rainwater intended for drinking should be tested so that any necessary filters to make it wholesome can be used in the system. Bacterial disinfection is also required and an ultraviolet filter or other treatment devices take care of this. The rainwater is also filtered on its way to the tank to remove coarse material like leaves.

Bear in mind that regular service and maintenance of the system is very important, and you should budget for this as well as the initial installation when you’re planning to get started with rainwater harvesting.