Rainwater harvesting - Cambridge Water

Rainwater harvesting

It is a well-known fact that much of the water we use does not need to be of drinking water quality. Studies have shown that 55 per cent of domestic treated water could be substituted for rainwater, while 85 per cent of water used for commerce and industry does not need to be of drinking water standard.

As global warming becomes increasing evident more and more architects and builders are turning to rainwater harvesting systems to help conserve water stocks.

How they work

In simple terms rainwater harvesting systems are designed to capture and store rainwater that falls onto the roofs.

Rainwater runs down the roof and into guttering and down pipes in the normal way. It is then passed through a filter to remove leaves and other debris, before being stored in an underground tank.

The water can be used, with or without the addition of a header tank, for a variety of non-potable water uses including flushing the toilet, washing vehicles and gardening.


Typically rainwater harvesting systems are more suited for new-build properties, where the cost of plumbing them in is negligible. Retrofitting them into an existing property can be expensive because of the amount of internal plumbing work required.

A full-rainwater recycling tank for a two-storey house with a 100m2 roof can cost in excess of £3000.


The British Standard for rainwater harvesting, BS8515 provides criteria for rainwater harvesting equipment manufactured in the UK.

For more information on rainwater harvesting please visit the Environment Agency website.