The short answer is: Yes, in the UK, it's legal and encouraged. But, like many things, there are important conditions, regulations, and best practices you need to be aware of.
1. Yes, you can legally Harvesting rainwater
According to the Environment Agency, you do not need a water abstraction licence to harvest rainwater — as long as the water you're collecting is purely rainwater (i.e., you’re not mixing it with river water, groundwater, or licensed sources).
Their Regulatory Position Statement makes it clear: if your storage system only contains collected rainwater, and you use that water without redirecting it into natural inland waterways or groundwater, you're fine.
However, if you mix harvested rainwater with surface or ground water in a reservoir that then drains into a watercourse, you do need an abstraction licence.
2. Why People Think It’s Illegal (and Why That’s Wrong)
Misunderstandings about rainwater harvesting often come from water-rights debates in other countries (especially the U.S.). Some US states do have strict water-rights laws, but that's not the norm in the UK.
In contrast, in the UK: Water companies and councils often promote rainwater harvesting. Some even offer incentives to do so.
The most commonly used are water butts (barrels attached to downpipes).
3. Regulations You Should Know About
Although it's legal, there are rules - especially when it comes to health, plumbing, and installation:
Water Fittings Regulations: The Water Supply (Water Fittings) Regulations (and byelaws in Scotland) apply to rainwater systems. If you plan to plumb harvested rainwater into your property (e.g., for flushing toilets), you need to comply.
Backflow & Cross-Contamination: Non-drinkable (“non-potable”) water from rain harvesting must not contaminate your mains water (drinking water). Pipes must be clearly marked, and there should be air gaps or other safeguards to avoid backflow. Rainwater pipe is usually marked as black pipe with a green stripe.
Building Regulations / Standards: For larger or more integrated systems, you’ll likely need to design according to best practice. For example, the British Standard BS EN 16941-1 covers design, installation and maintenance of rainwater harvesting systems.
Sustainable Drainage Systems (SuDS): National SuDS standards recognise rainwater harvesting systems as part of sustainable drainage, especially for new developments.
4. Health & Safety Considerations
Harvested rainwater is not automatically safe to drink. Unless you treat it (e.g., with UV filters, filtration), there’s a risk of contamination (e.g., bacteria, bird droppings).
Stored water (i.e. in tanks) comes with various risks including standing water which can support bacterial growth (e.g., Legionella), so maintenance of your tank, filters, and pipework is very important.
5. Planning Permission — Do You Need It?
In most cases, you don’t need planning permission to install a water butt or a small rainwater harvesting system.
However, for larger installations (for example, big underground tanks, or if you're in a listed building / conservation area), it's best to check with the planning office at your local council.
6. Best Practices
If you’re thinking of setting up rainwater harvesting:
Choose the right tank size: Calculate based on your roof area, rainfall, and likely water usage.
Use filtration: Even for non-drinking uses, filters help remove debris and improve water quality.
Maintain system regularly: Clean gutters, check your water tank, clean filters, and inspect pipework.
Tell your water company: Under the Water Fittings Regulations, you often need to inform your water supplier about non-mains water systems.
7. Why It’s Worth Doing
Save water & money: Using harvested rainwater for toilets, washing machines, or your garden reduces demand on mains water.
Environmentally friendly: Less reliance on treated water helps with sustainability and reducing runoff.
Resilience: In dry spells, having stored rainwater gives you extra flexibility.