A rainwater harvesting installer designs and installs systems that collect rainwater from roof surfaces, filter it and store it in a tank for non-potable uses such as toilet flushing, garden irrigation and washing machines. Systems must comply with BS 8515:2009+A1:2013 and Water Regulations to prevent cross-connection with the mains supply. A correctly designed system can offset 30-50% of a household's mains consumption and reduces surface water runoff.
What they do
- Roof catchment area assessment and water yield calculations
- Tank sizing to match demand and rainfall patterns
- Underground or above-ground tank installation
- First-flush diverter and filter installation
- Pump, controls and mains top-up installation
- WRAS-compliant backflow prevention to protect mains supply
- Pipework to toilets, irrigation outlets and washing machine feed
- Commissioning and maintenance advice
When you need one
A rainwater harvesting installer is needed when you want to reduce mains water use, meet planning conditions or manage surface water runoff on site.
Typical costs (UK, 2025)
| System type | Typical cost |
|---|---|
| Above-ground butt with gravity feed (garden only) | £500 - £1,500 |
| Below-ground tank, toilet flushing only | £2,500 - £5,000 |
| Whole-house below-ground system with pump | £5,000 - £10,000 |
| Commercial system (large roof, multiple uses) | £10,000 - £40,000+ |
| Mains top-up controller | £300 - £600 |
| Annual service and filter clean | £150 - £300 |
Costs depend on tank size, burial depth and pipework runs. Obtain at least two quotes from RHRA members.
Qualifications to look for
The Rainwater Harvesting Association is the UK trade body for the industry. Members commit to BS 8515 compliance and WRAS-approved practices. Check at rhra.org.uk.
Water Regulations Advisory Scheme approval confirms competence to install backflow prevention under the Water Supply (Water Fittings) Regulations 1999.
The British Standard for rainwater harvesting system design, installation, testing and maintenance. Ensure any system is designed to this standard.
How to find a reputable rainwater harvesting installer
Frequently asked questions
Do I need planning permission for a rainwater harvesting system?
In most cases no - underground storage tanks and internal pipework are permitted development. Listed buildings or conservation areas may need consent for visible external elements. Your installer should advise.
How much water can a rainwater harvesting system save?
A well-designed whole-house system can supply 30-50% of a household's total water demand. Toilet flushing alone accounts for about 30% of mains consumption, so even a WC-only system delivers significant savings.
What qualifications should a rainwater harvesting installer have?
Look for RHRA membership and compliance with BS 8515:2009+A1:2013. A WRAS-approved plumber is essential to ensure backflow prevention is correctly installed and the system cannot contaminate the mains supply.