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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.

Water Availability

The UK has an estimated water deficit of 5 billion litres per day in the next 25 years, according to the UK Environment Agency. Rainwater Harvesting reduces the usage of public water supplies by meeting up to 75% of the total water demand within a building with rainwater. 

Importantly, water savings are achieved without any changes to consumption habits from users. 

Discharge Rates

Large buildings provide ample roof space for collecting clean rainwater, allowing this precious resource to be reused to meet the large water demands of non-household buildings. Without reusing rainwater, these large volumes would be sent straight to the over-capacity drainage network. When drainage networks become overwhelmed, untreated sewage is released into surrounding water courses. 


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

Rainwater Harvesting is achieved in commercial properties through a variety of methods. 

Choosing the right system is crucial. Based on our maintenance expertise, the primary cause of systems failing is inadequate sizing of the internal equipment. While on paper, the system type may appear capable of delivering sufficient flow and pressure, in practice, an undersized system will struggle to meet water demands.

Our team of experts can size your system for you, ensuring water savings for the long term. See more below. 

 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.
  • Includes mains water protection through a fail-safe mechanical ball valve. 

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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

  • 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).
  • Includes mains water protection alerting users to a potential mains water leak. 

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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

  • 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.
  • Includes mains water protection through fail-safe mechanical ball valves. 
  • Unique ingress protection to prevent rodents from entering the system. 
  • Fail-safe dry run protection on the energy-efficient booster pumps. 

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 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.

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Technical Features 

PLC Controls: Smart system with easy-to-replace components, minimising downtime compared to more common PCB controllers.

Intelligent Systems: Centralised control panel ensures stability, easy monitoring, and minimal water supply disruption.

BMS Connectivity: Custom-designed to easily monitor storage levels, water consumption, faults, salinity levels, and temperature.

Mains Water Backup: Always prioritises rainwater but will automatically switch to mains water when necessary for a steady supply.

Mains Water Protection: Prevents mains water wastage with automatic shutoff valves and alerts, avoiding high water bills in valve failure scenarios.

Header Tank Optimisation: Smart controller ensures the header tank is always full, ensuring the system can keep up with demand.

Multi-Tank Compatibility: Works with multiple header tanks, reducing the need for multiple systems on large projects.

Further Information

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.

Why Choose Stormsaver?

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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