Rainwater harvesting is legal in the UK, and you do not need planning permission to collect rainwater for non-potable reuse in your business or home.
This rainwater harvesting regulatory guide UK explains how to collect, store and filter rainwater from roof areas for toilet flushing, irrigation, vehicle washing and laundry facilities.
In the UK, several standards and regulations govern rainwater harvesting, determining system sizing, implementation, maintenance and management.
In this guide, we provide a complete rainwater harvesting regulatory guide UK, covering current legislation and how the regulatory environment could evolve in the future.
What we’ll cover in this rainwater harvesting regulatory guide UK
- BS 16941-1:2024
- The National Standard for SuDS
- Part G of the Building Regulations 2010
- Water Supply (Water Fittings) Regulations 1999
- Water Supply (Water Quality) Regulations 2016
- Water Industry Act 1991
- Future UK rainwater harvesting regulatory environment
BS 16941-1:2024
BS 16941-1 is the technical standard for designing, sizing and maintaining rainwater harvesting systems in the UK.
A full sizing methodology is provided, based on storing 18 days’ worth of rainwater for non-potable use, ensuring supply during low rainfall.
The 2024 update incorporated a climate change simulation within the sizing approach.
BS 16941-1 applies to commercial systems, communal residential systems, and individual plot homes.
For more detail, read our full guide on BS 16941-1.
The National Standard for Sustainable Urban Drainage Systems (SuDS)
Rainwater harvesting systems are often a key part of drainage strategies within new planning applications.
Because of this, rainwater harvesting systems are assessed against the National Standard for SuDS, an approved code of practice for the design of sustainable drainage on new development schemes.
Within the standard, under Section 1.2, rainwater harvesting is prioritised as the primary runoff destination for stormwater. This means both commercial and residential schemes should utilise rainwater harvesting systems to successfully manage stormwater on site.
Furthermore, under Section 7.1, the rainwater harvesting system must have a maintenance and management plan that determines required remedials, servicing intervals, lifespan information and de-sedimentation.
We have produced a full guide to the National Standards for SuDS and rainwater harvesting here.
Water Supply (Water Fittings) Regulations 1999
- Regulation 5 – new rainwater harvesting systems must be notified to the local water supplier.
- Regulation 14 – public water supply must be protected by correct pipework and air gaps.
- Water companies may inspect systems for cross-contamination risks.
Water system inspections are completely normal and there is nothing to be concerned about. As part of the design process, we support best-practice advice on the necessary air gaps and pipework identification.
Here is a helpful resource by Water Regs UK to help you find out how to submit Notifications to your local water company.
Part G of the Building Regulations 2010
Part G covers water efficiency and water systems in new buildings. Rainwater harvesting, described as ‘water from reclaimed sources,’ is referenced.
Part G of the Building Regulations state that rainwater harvesting systems must be compliant with BS 16941-1 in order to be deemed safe within a building.
While not yet mandatory within Part G, the UK Government is consulting on compulsory water reuse.
Water Supply (Water Quality) Regulations 2016
These regulations currently only set quality standards for the public (drinking) water supply and do not directly apply to rainwater harvesting.
It is hoped that future ammendments to these regulations could include a set quality standard for non-potable water.
Water Industry Act 1991
The Water Industry Act governs how water companies operate in the UK. Whilst this legislation is not applicable to implementing rainwater harvesting in a non-household setting, it does apply to the adoption of multi-plot communal rainwater harvesting systems.
Sections 67 & 68 require water supplied for domestic purposes to be wholesome, and section 218 covers the definition of domestic purposes. This definition includes toilet flushing.
Future amendments could allow communal rainwater harvesting systems, as investigated under the Revised Environmental Improvement Plan 2025.
Future rainwater harvesting regulatory environment UK
Mandatory water reuse in the UK
Rainwater harvesting and greywater recycling is best installed at the new build design stage. Whilst retrofitting is possible, it is complex and can cost on average 50% more. Including rainwater harvesting in all new buildings between 2026–2050 could reduce the national water deficit by 20.5%.
A single approved code of practice
Currently the technical standard for rainwater harvesting is a paid document by the British Standards Institution. As plumbers will need to access this document, the Drinking Water Inspectorate have recommended a readily available document be made available on the UK Government website, similar to that of the National Standards for SuDS. This would include set quality parameters for non-potable water.
Water reuse included as part of the WaterSafe training programme
We believe that only trained, qualified practitioners should be able to install and maintain rainwater harvesting systems in the UK. Extending the WaterSafe scheme will help to minimise the risk to public health.
Water companies to be allowed to adopt communal water reuse schemes
Changes to the Water Industry Act 1991 to allow water companies to adopt communal rainwater harvesting systems is key. This would provide a clearly defined dual pipe network of potable and non-potable water.
Mandatory pipework and identification as part of the Water Fittings Regulations
Standardising non-potable water pipework to align with that of European countries would successfully reduce risk to public health. For example, other countries across Europe use solid purple coloured pipework to highlight the presence of non-potable water.
Summary and next steps
Commercial and Non-Household rainwater harvesting systems and residential systems for individual plots are currently acceptable to install under the UK regulatory framework. However, communal schemes for residential developments cannot currently be adopted by water companies, limiting the ability to install such systems.
The English and Welsh Governments are currently investigating how communal rainwater harvesting systems can be implemented safely and how the legislative landscape may evolve. Collectively, the Cunliffe Report, the Revised Environmental Improvement Plan and the recent Drinking Water Inspectorate report highlight these ambitions.
We are encouraging design engineers, water companies and developers to include rainwater harvesting or greywater recycling on as many projects as possible. Any building now built without water reuse compounds the problem of water scarcity. To get design and implementation advice, book on to one of our free CPDs.
