Harvesting Rainwater for Domestic Uses: An Information Guide (2010)

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This publication carried out by the Environment Agency examines rainwater harvesting systems for non-potable domestic uses in houses and gardens. This guidance is for homeowners, house builders, planners, plumbers, architects and building managers. It contains information on the benefits of rainwater harvesting systems, their design, installation, maintenance requirements and cost. It also contains examples of systems that have been installed and are in use. Many of the concepts discussed can also be applied to industrial and commercial premises.

1 Introduction

This publication examines rainwater harvesting systems for non-potable domestic uses (those that do not require water suitable for human consumption) in houses and gardens. Many of the concepts can also be applied to industrial and commercial premises. This guidance is for homeowners, house builders, planners, plumbers, architects and building managers. It contains information on the benefits of rainwater harvesting systems, their design, installation, maintenance requirements and cost. It also contains examples of systems that have been installed and are in use.

This guide does not cover recycling of water, for example, from sources like the bath and shower (greywater). This is examined in a separate publication1.

1.1 What is rainwater harvesting (RWH)?

Rainwater harvesting is the collection of rainwater directly from the surface(s) it falls on. This water would otherwise have gone directly into the drainage system or been lost through evaporation and transpiration. Once collected and stored it can be used for non- potable purposes. These include toilet flushing, garden watering and clothes washing using a washing machine. You should note that where used for washing machines, if the quality of the collected water is poor, there can be issues with both colour and odour.

1.2 Why consider a RWH system?

Despite the common perception that it rains a lot in England and Wales, our water resources are under pressure. A high volume of water is taken from the environment for human use. Demand for water is rising because the population is increasing, lifestyles are changing and the impacts of a changing climate are becoming more clear. In the South East of England, where large numbers of people live and work, water is scarcer than anywhere else in England and Wales. In fact, there is less water available per person in this region than in many Mediterranean countries.

We need to plan carefully for the future to ensure reliable water supplies are available for everyone whilst protecting the natural environment.

The Environment Agency advocates the ‘twin track’ approach of developing resources and managing demand. Exploring ways to reduce demand for mains water is essential to ensure a sustainable future for water resources. One of the options is to install RWH systems to substitute mains water use for purposes where drinking water quality is not required.

1.3 What savings can be achieved?

Any RWH system will reduce the dependence on the mains water supply.

Potential savings need to be assessed on an individual basis before any system is implemented. Factors which will influence this are; the demand for non-potable water, the amount of rainwater that can be collected and supplied and whether the property is charged by volume of water used (is metered).