Why recycle rainwater?
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

  • The most reliable type of commercial rainwater harvesting arrangement.
  • Ideal for providing high-flow rates of recycled rainwater for the largest water users.
  • Rainwater is fed from the main storage tank into a secondary header tank. 
  • Header tanks can gravity-feed rainwater to outlets or be in a low-level plant room with a booster pump.
  • Our intelligent control panel will automatically supply mains water into the header tank when rainwater is limited.
  • Highly efficient water-saving arrangement due to the mains water top up filling a small surface area of a header tank.
  • Can continue to supply outlets with water during maintenance disruption.

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

Pressurised Systems

  • The most compact rainwater harvesting solution, ideal for small buildings with no more than 10 toilets.
  • Rainwater is supplied from the main storage tank via a set of submersible pumps and a pressure vessel.
  • Our intelligent control panel will supply mains water into the main storage tank via an air gap when no rainwater is available.
  • Specifying this system comes with a cautionary note. There will be no water supply available during unplanned maintenance downtime (use the below Combi approach for high levels of reliability).
  • Limited water-saving efficiency due to the mains water top up being required to fill a larger surface area within the main storage tank (use the below Combi approach for high levels of efficiency).

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

Combi Systems

  • A simple-to-install method of reusing rainwater within large buildings.
  • A pre-wired, pre-built, pre-tested control unit often used in schools, distribution centres, offices, and many other building types. 
  • Rainwater is supplied from the main storage tank into the Combi Control Unit. The Combi Unit houses an integrated break tank, energy-efficient variable speed booster set, and system controls.
  • The Combi Control unit is supplied in a range of common capacities. This refers to the capacity of the integrated break tank, including 225, 400, and 620 litres.
  • Our intelligent controls will supply mains water into the Combi Control Unit when rainwater supplies are limited. This is done via a WRAS compliant air gap with ingress protection.

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

StormStation Systems

  • The simplest way of achieving rainwater harvesting.
  • Can be used in most building types, for portable use, and as a retrofit solution.
  • A self-contained rainwater harvesting system in a plug-and-play unit.
  • StormStation houses filtration, a main storage tank, mains water top up tank, controls, and a pump set to supply rainwater to the building.
  • Supplied in a range of capacities covering the most common main storage tank sizes in the UK, between 3,000-20,000 litres.
  • StormStation can be supplied with photovoltaics for a carbon-neutral rainwater supply.
  • Includes UV circulation to ensure the rainwater within the unit is constantly flowing to prevent stagnation and bacteria growth.

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Further Information

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.

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.

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.


  • 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.
 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. 

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Constructionline Gold Member CHAS Accredited UK Rainwater Harvesting Association Member Safecontractor Approved Waterwise Affiliate UK Business Awards Winner 2022