A diagram of a commercial rainwater harvesting system. rainwater collected from the roof and collected into a central tank to supply toilets

A rainwater harvesting system in a car wash depot

a rainwater harvesting system control unit in a plant room of a building supplying recycled rainwater to toilets

Commercial Rainwater Harvesting

Commercial or non-household rainwater harvesting is a cost-effective solution for collecting, attenuating, and reusing large volumes of rainwater from the roof area of large buildings to provide a non-potable water supply. Recycled rainwater can be used for toilet flushing, irrigation, vehicle washing, cooling, and many other industrial uses.

Recycled rainwater supplied by a commercial rainwater harvesting system provides an alternative to public water supplies, assisting with the prevention of water scarcity, all whilst reducing stormwater runoff from the site by managing rainwater locally. Discover how our UK-manufactured systems can help to kickstart your water-saving journey today. Find out more below.

get a quote case studies

Why recycle rainwater?

Reduce the waste of precious drinking water, alleviate flooding, and prevent pollution.

How Commercial Systems work

Why include rainwater harvesting in commercial projects

With an estimated water deficit of 5 billion litres per day in the next 25 years, according to the UK Environment Agency, and with increasing capacity issues within combined drainage infrastructure, installing rainwater harvesting in large buildings is crucial.

Large buildings provide ample roof space for collecting perfectly clean rainwater, allowing this precious resource to be reused to meet the large water demands of typical non-household buildings. Without reusing rainwater, these large volumes of rainwater would be wasted and enter the over-capacity drainage network.

Rainwater harvesting is now commonplace in many types of buildings, including schools, hospitals, distribution centres, leisure venues, and manufacturing facilities. Rainwater harvesting can even be combined with our on-site attenuation and greywater recycling technologies for buildings with considerably large water requirements.

Live monitoring of Stormsaver’s 2,000 installations shows an average water saving of 75 percent. Discover some of our case studies here.

Our Commercial System Types

If you are unsure which system is right for you, our experienced team can design, supply, and install the most efficient solution for your project. All our systems are UK manufactured by us here in the UK and draw upon our two decades of experience as a manufacturer and maintenance provider, giving you confidence in the integrity of your new sustainable water supply. Tell us about your project here.

A non pressurised rainwater harvesting system in a supermarket. this supplied recycles rainwater to the toilets

Non Pressurised Systems

Most common commercial rainwater harvesting arrangement.
Suited to buildings with large-scale water needs.
Rainwater flows from the main tank to the secondary header tank.
Header tanks gravity-feed or use booster pumps.
Smart controls automatically switch to mains when rainwater is low.
Highly efficient arrangement due to mains water topping up the header tank.
Uninterrupted supply during maintenance and component failure.

get a quote

A pressurised rainwater harvesting system diagram. Showing rainwater being collected into a tank and boosted via at pressure to points of use.

Pressurised Systems

Compact solution ideal for small buildings (below 10 toilets).
Rainwater is supplied via submersible pumps from the main storage tank.
Mains water tops up via the main rainwater storage tank.
Internal capacity is achieved through a suitably sized pressure vessel.
Smart controls automatically switch to mains water when rainwater is low.
Caution: does not supply water during maintenance (consider Combi approach).
Limited saving efficiency due to mains water topping up large surface area (consider Combi approach).

get a quote

A combi rainwater harvesting diagram showing rainwater collected from the roof area and being boosted via a control unit to use points

Combi Systems

Compact solution for large buildings with large water demands.
Ideal for supermarkets, leisure centres, and offices.
Pre-wired control unit for simple installation.
Combi Control Unit integrates a header tank, booster set, and controls.
Available in different tank capacities: 225, 400, and 620 liters.
Intelligent controls tops up the combi unit with mains water when rainwater is low.

get a quote

a self-contained rainwater harvesting system recycling rainwater in a petrol service station

StormStation Systems

The simplest to install rainwater harvesting method.
A versatile unit, usable in various building types, for portable needs, and as a retrofit solution.
A self-contained system which includes filtration, main storage tank, top-up tank, controls, and pump set.
A plug-and-play unit supplying rainwater to buildings.
Supplied in a range of capacities: 3,000-20,000 litres, covering common UK rainwater tank sizes.
Option for photovoltaics for a carbon-neutral water supply.
Includes UV circulation to prevent stagnation and bacteria growth.

get a quote

Further Information

How commercial rainwater harvesting works

Collection – rainwater is collected via the large roof space and channelled into roof drainage points. Roof drainage points should enter the ground via sealed gullies to prevent contamination from surface water which has a higher potential for pollutants.

Pre-tank filtration – As per BS 16941:2024, the British Standard for Rainwater Harvesting, all rainwater will first pass through a mesh pre-tank filter rated to 1000 microns. This pre-tank filter should always be located before rainwater enters the main storage capacity.

Main storage tank – After passing through the pre-tank filter, rainwater enters the main storage tank via a calmed inlet. This prevents the disturbance on the base of the storage tank. Rainwater then passes through a floating suction filter and is boosted internally via a set of submersible pumps.

Internal storage and control panel – The best designs of a rainwater harvesting system will have internal storage capacity where the automatic mains water top-up is located. When there is a drought period and no supply is available, the mains water top-up will continue to provide a water supply to usage points. Our system arrangements overview above shows the different methods of achieving internal storage and controls.

Additional filtration – some projects demand an optional third stage of filtration. This can be either achieved via our low-maintenance automatic backwash. Learn more here. Or via traditional cartridge filters which prevent important components from fine debris.

Sizing information for specifiers

Stormsaver will provide you with the most efficient system and sizing requirements.

We look at sizing a rainwater harvesting system in two ways, according to the British standard BS 16941:2024 for rainwater harvesting.

1: Collection potential – Being realistic about how much rainwater lands on a roof area is important. We want to ensure the rainwater storage tank overflows on occasion to ensure the rainwater within is always suitably circulated.

2: Demand within the building – We will consider how much water the system will need to supply for the building. This includes considering the applications within the building.

Internal storage tank sizing – Surprisingly, the British Standard does not cover internal storage sizing, but under-sizing this important element of the rainwater harvesting system is the biggest reason why systems fail here in the UK. Our experts will suitably size this for you.

Combining with attenuation - Rainwater harvesting can be combined with on-site attenuation via Active Attenuation technologies. Where Active Attenuation is being used, the total storage capacity of the main storage tank (or crates) will be the equivalent of the roof area attenuation capacity for the site. This calculation will be completed by the drainage consultant on the project.

Best practice tips for specifiers

Include a third stage of filtration

Stormsaver offers unique Automatic Backwash filtration which offers autonomous self-cleaning to achieve a third-stage of filtration.
Protects water meters and other important components from installation debris, and small particles.

Prevent shadowing in UV disinfection.

Ensure internal storage is sized correctly

The break tank, header tank, or pressure vessel should be sized by our specialist team.
Undersizing this important capacity is the biggest reason why systems fail.

Maintenance

Always ensure that the pre-tank filter and submersible pumps are accessible from the finished ground level. Instances, where these components are located deep within storage tanks, have resulted in costly confined space equipment being required during maintenance.

Downloads

Technical Data Sheets

Data Sheet - Combi Control Unit 225 Litre for Rainwater Harvesting

Data Sheet - Combi Control Unit 400 & 620 Litre for Rainwater Harvesting

Data Sheet - Singlex Control Unit for Non-Pressurised Rainwater Harvesting

Data Sheet - Singlex Control Unit for Pressurised Rainwater Harvesting

Data Sheet - StormStation Rainwater Harvesting 3,000-5,000 Litre Carbon Neutral

Data Sheet - StormStation Rainwater Harvesting 5,000-20,000 Litre Carbon Neutral

System Schematics

System Schematic - Non-Pressurised Rainwater Harvesting Below Ground

System Schematic - Non-Pressurised Rainwater Harvesting Above Ground

System Schematic - Combi Rainwater Harvesting Below Ground

System Schematic - Combi Rainwater Harvesting Above Ground

System Schematic - Pressurised Rainwater Harvesting Above Ground

System Schematic - Pressurised Rainwater Harvesting Below Ground

System Schematic - StormStation Rainwater Harvesting

Rainwater harvesting control unit diagram. Image shows internals, including filters and controls.

Our Added Value Options

Looking for additional filtration, UV disinfection, or installation services? Our added value options give you access to best-practice approaches. Learn more here.