Rainwater Harvesting

Green House

Rainwater harvesting is capturing, storing and reusing rainwater.

In many parts of the world, rainwater harvesting is one of the prime sources of clean water. Here in the UK, domestic harvesting of rainwater has traditionally been used for providing water for gardening. However, there is a lot of other uses for harvesting rainwater in and around the home.

Why rainwater harvesting?

World wide, water is increasingly becoming a scarce resource. A combination of climate change and poor management is leading to shortages in many countries - including here in the UK.

In London alone, leaks from aging mains are wasting enough water to fill 300 Olympic swimming pools every single day. Many major cities use more water than can now be replenished from natural sources.

Meanwhile, Africa and Southern Europe are becoming drier as a result of global warming and in North America and Northern Europe, the glaciers that provide a significant amount of fresh water are shrinking.

Over the next few years, it is likely that more hosepipe bans will be put in place and water prices will continue to rise as our own supplies struggle to cope with demand.

Against this backdrop, harvesting rainwater can help reduce our own personal usage and reliance on mains water, saving money and helping the environment at the same time.

How do rainwater harvesting systems work?

There are many types of rainwater harvesting systems. The most common are rooftop and runoff rainwater systems.

Harvesting rooftop rainwater is typically the most economical system and the most common system used for homes. Rainwater is collected from the roof and captured in a large storage tank often underground.

Runoff rainwater systems capture rain from a mountain or hillside, capturing the rainwater in a reservoir. Whilst some houses are able to take advantage of a runoff system, these systems are typically used where much larger volumes need to be captured providing water for a village or small town, for instance.

Once the rainwater has been captured, it can then be used as is, for watering the garden or filling a garden pond; or it can be filtered and used inside the house as a secondary water supply.

What is rainwater used for?

Large scale rainwater harvesting systems are often used as the main supply of water. In New Zealand, for instance, many small villages rely entirely on harvesting rainwater for all their water requirements.

Most household rainwater harvesting systems do not use the rainwater for drinking water. Instead, a secondary water system is installed in the house and the rainwater is used for washing or flushing the toilets.

It has been calculated that around 1% of water treated in the UK ends up being drunk. The remainder is used for washing, flushing toilets or is wasted through leakage. Harvesting rainwater for these purposes can save a considerable amount of mains supplied water and in many cases can offer a significant cost saving.

What rainwater harvesting systems are available?

First of all, you need to decide what you want to use rainwater for.

Using rainwater outside

The most common use for harvesting rainwater is for an outside water supply. Watering the garden, washing the car, cleaning the patio, topping up the pond, cleaning muddy boots and hands can all be done using rainwater with minimal filtering of the rainwater first.

The most basic harvesting system is a traditional garden water butt, attached to a down pipe connected to your household guttering. Prices start from around £25 for a 100 litre water butt, which will give you a basic harvesting system for capturing rainwater which can then be used for replenishing pond water levels and watering the garden using basic irrigation methods or in conjunction with a watering can.

A simple upgrade to a water butt is the addition of a simple harvesting rainwater pump and filter. This creates a pressurised system that can then be used in conjunction with a hosepipe: great for watering the garden or washing the car using a hosepipe. These rainwater pumps and filters start from around £40.

Such a system will enable a homeowner to avoid hosepipe bans - which are likely to become more common and more stringent in the years to come.

Using rainwater in the house

Rainwater can be used in the house to supply washing machines and toilets - and even showers and baths if you want. The rainwater is filtered and siphoned in order to clean it making it ideal as a source of non-drinking water.

A large rainwater tank is installed next to the house, either above or below ground and typically capable of holding between 1,600 and 7,000 litres of rainwater. This rainwater is filtered and pumped into a header tank in the loft of your home where it is distributed into a household non-drinking supply.

Some modifications will be required to your internal plumbing in order to separate the rainwater supply from your fresh water supply.

These systems include automatic switchover so that the system can switch from rainwater to mains water if there is insufficient rainwater in the system and the tank runs dry.

Are rainwater harvesting systems the same as water recovery systems?

No, although water recovery systems are often used in conjunction with rainwater harvesting systems.

Water recovery systems recover the waste water known as 'grey water' that we use in our homes and use it for a second time. Typically this means water used from washing machines, baths and showers is filtered and then used to flush the toilets.

Whilst efficient, water recovery systems can be difficult to install in an existing house. They are worth considering in a new build where all the necessary plumbing can easily be installed at comparatively low cost.

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