How to make a rainwater collection system?

Making your own rainwater collection system is a rewarding DIY project. Systems range from the very simple to the highly sophisticated, and you can build one at almost any skill level and budget.

The Simplest System: A Water Butt

The easiest way to start is with a single water butt connected to a downpipe. You need a water butt, a downpipe diverter kit, and optionally a stand. Position the butt on a firm, level surface close to a downpipe. Install the downpipe diverter by cutting a section from your downpipe with a hacksaw, then fitting the diverter. Connect the diverter hose to the butt inlet. Fit the lid securely and position the overflow away from foundations.

Intermediate System: Multiple Interconnected Butts

For greater storage capacity, connect multiple water butts together using linking kits. Place the first butt at the highest point and subsequent butts at progressively lower levels so water flows between them by gravity. You can also divert multiple downpipes around your house into your interconnected network. This modular approach provides significant storage without the expense of a single large tank.

Advanced Above-Ground System with Pump

For pressurised water for a hose or sprinkler system, use a larger above-ground tank (1,000 to 5,000 litres) with a pump. Choose a UV-stabilised polyethylene tank on a proper base. Install the tank connected to one or more downpipe diverters. Fit a submersible or external pump with appropriate power supply and a float switch to prevent running dry.

Complete System with Filtration for Indoor Use

For the most advanced DIY system supplying indoor appliances, start with a tank of 3,000-10,000 litres. Install downpipe filters and a pump sized for your needs. After the pump, install sediment filtration, carbon filtration, and UV disinfection. Include mains water backup with a non-return valve. This requires competent DIY skills and understanding of water regulations.

Planning and Regulations

Before building any rainwater collection system, check with your local building control department about requirements. For systems that connect to internal plumbing, you must comply with the Water Supply (Water Fittings) Regulations 1999, which require appropriate backflow prevention and labelling of non-potable water pipes. The British Standard BS 8515:2009 covers rainwater harvesting systems and provides design and installation guidance. If you live in a conservation area or listed building, check whether external tanks require planning permission. For most domestic systems, planning permission is not needed, but large above-ground tanks visible from the road may require approval. By following these guidelines and building your system carefully, you can create a rainwater collection system that provides free, soft water for years to come.

Scaling Up Your System Over Time

One of the advantages of DIY rainwater collection is the ability to scale up gradually. Start with a single water butt to learn the basics and assess how much water you actually use. After a season of experience, evaluate whether more storage would be beneficial. Add a second butt connected to a different downpipe, or interconnect additional butts to your existing system. As your confidence grows, consider upgrading to a larger tank with a pump for pressurised water. Eventually, you may progress to a comprehensive system with underground storage, filtration, and indoor plumbing connections. This incremental approach spreads the cost over time and allows you to learn from experience at each stage, ensuring you make the right decisions for your specific property and needs.