How Rainwater Harvesting is done

Rainwater is channelled into roof drainage points and is collected in a central rainwater storage tank which can be located above or below ground.

All rainwater is processed through a mess filter prior to entering the central storage tank to remove larger leaf debris. The mesh filter in a rainwater harvesting system should be rated to 1000 microns as per the British Standard (1mm).

Rainwater enters the central storage tank via an inlet calmer preventing finer sediment on the base of the central storage tank from being disturbed.

In the event of the storage tank becoming full, an automatic overflow ensures excess rainwater is channelled into the drainage system. The overflow is complete with a none-return valve arrangement to ensure no objects can enter the rainwater harvesting storage tank.

The rainwater harvesting storage tank contains level sensors and submersible pumps which, when a demand for water is detected by the control panel, will take water from the cleanest part of the tank via a floating suction filter.

Reclaimed rainwater is then distributed to a pressurised control panel or break tank via the submersible pump. An optional third stage of filtration is recommended at this point in the form of UV filtration and automatic backwashing. Automatic backwashing filters rainwater to 35 microns removing any finer particles from the rainwater.

Reclaimed rainwater is then boosted to points of use via the rainwater harvesting control panel to supply non-potable applications, including toilets, urinals, irrigation systems, vehicle wash plants and laundry systems.

Non-pressurised rainwater harvesting systems will rely on a header tank to gravity feed rainwater to points of use rather than using a booster pump arrangement.

Learn more about the different types of rainwater harvesting systems available here.


rainwater harvesting systems


 Rainwater harvesting system with an above ground storage tank in a office building

Considerations for Rainwater Harvesting

Rainwater Harvesting Systems should be sized by a professional, like Stormsaver, who will consider a number of factors, including roof area, local rainfall data, building occupancy and water demand. These considerations will inform the size and type of rainwater harvesting system which will harvest the most rainwater for the building.

There are a number of different types of rainwater harvesting system available depending on the site requirements. The most popular form of rainwater harvesting system in the UK is a combi arrangement.

Combi rainwater harvesting system combines technologies from both gravity-fed systems and directly pressurised systems. Unlike gravity-fed rainwater harvesting systems, the combi arrangement does not require larger header tank to supply the rainwater to points of use. Learn more about Combi systems here.




Can Rainwater Harvesting supply…


Rainwater Harvesting can provide a sustainable water supply for toilet and urinal flushing. The number of toilets and urinals which are reliant upon a water supply from the rainwater harvesting system will be considered when sizing the system to ensure the total demand can be covered. It is recommended that rainwater harvesting systems supplying toilets should be properly maintained by a specialist, like Stormsaver, to reduce the likelihood of disruption from unexpected downtime.

Where a rainwater harvesting system supplies multiple toilets, it is also recommended that one of the toilets is reliant solely on a mains water supply to prevent the building from closure in the event of system downtime.

Irrigation and Gardening

A popular use of reclaimed rainwater from rainwater harvesting systems is for irrigation and garden watering. Potable water quality is not needed for this activity, therefore reclaimed rainwater is ideal. When the system is being sized the total number of outlets and usage period will be considered to ensure there is enough supply. Rainwater harvesting systems are sized based on 18 days storage capacity to ensure a sustainable water supply can be used during dry spells.

For prolonged periods of droughts an automatic mains water top up will ensure a constant water supply.


Rainwater Harvesting can be useful for many non-potable manufacturing processes. Businesses with a large water consumption can benefit from a rainwater harvesting system to improve water efficiency and reduce water bills. It is recommended that rainwater harvesting systems which provide a sustainable water supply for manufacturing should include ultraviolet filtration with an automatic backwash system. These additional filtration devices will ensure high levels of water quality.

Rainwater Harvesting Systems have been combined with reverse osmosis systems for large-scale manufacturing processes.


Portable Rainwater Harvesting Systems are available to supply sustainable water supplies for dust suppression. StormStation Rainwater Harvesting Systems can supply site welfare cabins with water supply for toilet flushing. StormStation can be easily moved upon completion of the construction project and transported to the next construction site. Learn more about StormStation here.


Rainwater Harvesting Systems provide a non-potable water supply which is not suitable for human consumption, therefore rainwater harvesting systems should not be connected to showers or baths under any circumstances in the UK. The British Standards enforces the ruling that rainwater harvesting systems should only be used for non-potable uses.

Drinking Water

Rainwater Harvesting Systems should not supply drinking water outlets in the UK. This is in line with the British Standard. Whilst reclaimed rainwater appears clean and clear, car fumes, avion faeces and other debris can enter the rainwater when it is collected from the roof area.

Rainwater Harvesting Explanation Video

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