Home & garden · Rainwater harvesting · UK guide
DIY Rainwater Harvesting: How to Collect and Use Rainwater at Home
From a simple water butt beside your downpipe to a large tank supplying garden irrigation, rainwater harvesting can reduce your reliance on mains water. Here’s how the systems work, what you can safely install yourself, and when a professional is needed.
1. Which rainwater collection system should you choose?
| System | Typical use | DIY suitability |
|---|---|---|
| Water butt, 100–300 litres | Watering cans, small gardens | Usually a straightforward DIY job |
| Linked butts or 500–2,500 litre tank | Vegetable gardens, greenhouse, irrigation | Often possible with appropriate foundations, overflow and fittings |
| Underground or whole-house system | Toilet flushing, some laundry applications and large-scale storage | Professional design and installation strongly recommended |
For most homes, a water butt and rain diverter are the simplest and lowest-cost place to start. Larger systems are worthwhile where you have significant garden demand and space for safe storage. Indoor use is more complex and not necessarily cost-effective.
2. How much rainwater could your roof collect?
A useful estimate is roof catchment area (m²) × rainfall (mm) × collection efficiency. One millimetre of rainfall over one square metre is one litre of water. A planning efficiency of 0.8 allows for some losses, but actual performance varies with roof, guttering and weather.
For a basic garden setup, begin with 200–300 litres. For frequent summer watering, consider 500–1,000 litres or more if the roof catchment, site and budget justify it. Storage size should reflect dry spells and your daily demand, not just annual rainfall.
3. How to install a simple water butt yourself
Difficulty: beginner to intermediate · Typical time: around 1–2 hours for a straightforward installation · Tools: tape measure, spirit level, marker, suitable saw or hole saw, eye protection and the manufacturer’s instructions.
- Choose the downpipe. Use a suitable roof gutter and check the downpipe material and diameter match the diverter. Avoid roofs likely to introduce unusual contamination.
- Prepare a firm, level base. A full 210-litre butt holds roughly 210 kg of water, before the container and stand. Use a load-bearing slab or suitably prepared foundation; never put a full butt on unstable blocks or soft soil.
- Position the butt and stand. Leave enough room for a watering can below the tap, with access for cleaning and maintenance.
- Fit the diverter. Follow the specific diverter’s cutting measurements and installation instructions. Do not assume every model uses the same height or hole size.
- Connect the hose. Keep it free of kinks and check all seals and fittings. A correctly installed diverter may return excess flow to the downpipe when the butt fills; otherwise a separate safe overflow is essential.
- Fit a secure lid and screen. Keep out leaves, animals and insects; reduce light entering the tank.
- Test with water. Check leaks, the tap, overflow and where excess water drains. Never direct overflow towards your home’s foundations or a neighbouring property.
Medium Harcostar 227L Water Butt, Stand and Diverter Kit Recyclable & Recycled Plastic Green Original Organics
A practical starter kit with stand and diverter; check included components before buying.
View at Water Butts Direct ↗
Harcostar Universal Rain Trap Diverter Original Organics
Simple diverter for a compatible downpipe; check diameter and installation requirements.
View at Water Butts Direct ↗
Gutter Mate Diverter & Filter in Black
Diverter with filter for reducing debris entering a water butt.
View at Water Butts Direct ↗4. Building a larger DIY garden rainwater system
If one butt runs dry too quickly, you can link compatible containers or install a larger above-ground tank. A typical arrangement is:
Roof → gutter → debris filter/diverter → covered tank → tap or pump → watering can or irrigation line. Provide a designed overflow to an appropriate drainage destination.
- Choose capacity and location. Ensure the tank is rated for above-ground use and accessible for maintenance. A 1,250-litre tank contains about 1.25 tonnes of water when full.
- Prepare the foundation. Follow the tank maker’s requirements for a level, structurally adequate base. Large tanks may require a professionally specified concrete slab.
- Filter incoming water. Fit a leaf/debris filter compatible with the tank inlet and roof runoff. Consider whether first-flush diversion is appropriate for your catchment.
- Plan overflow before filling. Make sure it can cope with heavy rainfall and will not cause flooding or damp.
- Choose how to draw water. A low tap works for filling watering cans. A pump can help with irrigation, but check flow, head, electrical protection and pump compatibility.
- Commission and test. Fill gradually, check stability and leaks, and verify that filters and overflow work.
Enduramaxx 720L Vertical Rainwater Tank
720-litre above-ground tank for larger garden storage; verify footprint and fittings.
View at Water Butts Direct ↗
Enduramaxx 1,250L Vertical Rainwater Tank
1,250-litre storage option for households with more outdoor demand.
View at Water Butts Direct ↗
Water Butt Linking Kit – 50cm Hose Black Original Organics
Link compatible water butts; check fitting size and tank compatibility.
View at Water Butts Direct ↗
GPS-100 230v Light-Duty Submersible Water Butt Pump Blue Original Organics
Submersible pump option for garden water distribution; electrical installation must be safe.
View at Water Butts Direct ↗5. How a professionally installed home system works
A professional rainwater harvesting system can supply non-drinking-water uses such as toilet flushing and certain laundry systems. The typical design includes roof collection, pre-filtration, an appropriately sized storage tank, a pump and controls, a separate non-potable pipe network, overflow arrangements, monitoring and a compliant mains-water backup arrangement.
A specialist should assess local rainfall and demand, roof materials, ground conditions, access, maintenance, plumbing separation and electrical safety. In England and Wales, connecting an alternative water system to building plumbing may require advance notification to the water supplier. Any mains-water top-up must have suitable protection against contamination, commonly a compliant air-gap arrangement for this high-risk application.
For domestic non-potable rainwater systems, professionals can use BS EN 16941-1 as a relevant design standard. Specialist plumbing, underground excavation and electrical connections are not good beginner DIY projects.
Is a professional system financially worthwhile? It depends on water use, metering, installation cost and ongoing pump/maintenance costs. For many households, a basic garden system is the simpler economic choice.
6. Recommended equipment checklist
| Component | Suggested option | When needed |
|---|---|---|
| Starter butt with stand | 227L Harcostar water butt kit | Small gardens |
| Space-saving butt | 110L slimline water butt kit | Narrow side passages |
| Large above-ground tank | 720L Enduramaxx tank | Higher garden demand |
| Extra-large tank | 1,250L Enduramaxx tank | Large gardens with suitable base |
| Downpipe diverter | Harcostar rain trap diverter | Connecting gutter to butt |
| Filter/diverter | Gutter Mate diverter and filter | Reducing incoming debris |
| Butt linking hose | 50cm water butt linking kit | Joining compatible butts |
| Garden pump | GPS-100 submersible pump | Pumped watering where suitable |
| Tank overflow fitting | Overflow syphon | Only where compatible with tank and drainage design |
These are examples from our current Water Butts Direct affiliate selection, not a universal bill of materials. Verify dimensions, included fittings, compatibility, suitability and current price with the retailer. Electrical, structural and plumbing requirements vary by installation.
7. Maintenance: keep the system useful and safe
- Inspect and clear roof gutters, leaf guards and inlet filters regularly, especially after storms and autumn leaf fall.
- Keep lids closed and openings screened to reduce insects, debris and animal access.
- Check stands, foundations, seals, hoses, pumps and overflow routes for movement or damage.
- Follow the manufacturer’s cleaning and winterisation guidance, including frost protection where needed.
- Clearly label non-potable outlets and prevent accidental drinking or cross-connection with mains water.
Frequently asked questions
Can I legally collect rainwater in England?
Generally, collecting roof rainwater for your own use does not require a water abstraction licence. Other rules may apply to plumbing installations, drainage changes and some larger or unusual systems.
Can I use rainwater to water vegetables?
Rainwater is commonly used for garden irrigation, but roof runoff can contain contaminants. Keep tanks clean and covered, avoid spraying edible leaves close to harvest, and use appropriate precautions for food crops.
Can I drink rainwater from a water butt?
No. Treat water collected in an ordinary water butt as non-potable. Drinking-water use requires an appropriately designed, tested and maintained treatment and supply arrangement.
Do I need a pump?
Not for filling a watering can from a raised butt with a tap. Pumps are useful for higher flow or pressure requirements, but must match the system.
Should I choose DIY or professional installation?
A simple outdoor water butt is usually a reasonable DIY project. Large tanks can be DIY only where the base, plumbing, overflow and electrical arrangements are within your competence. For underground storage or indoor non-potable plumbing, use appropriately qualified professionals.
Further guidance
For installation and safety guidance, see Wessex Water’s water butt guide, the RHS rainwater advice, UK Water Reuse Association, and Environment Agency guidance.
Information applies primarily to UK domestic installations, with legal references focused on England and Wales where indicated. This is general guidance, not a substitute for a site survey, manufacturer instructions or qualified professional advice.