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06 Aug 2021

Filtration - A journey of water

It is no secret that water quality is an essential requirement of any rainwater harvesting system, but why is it so important? Our focus this week at Stormsaver shines a spotlight on the importance of filtration, the crucial tool to maintaining optimum water quality levels. No matter who supplies your rainwater harvesting system you should consider what filtration you need and the costs and requirements of maintaining your filtration components.

With high water quality levels being reliant on robust filtration components, this blog will detail the different stages of the process from roof collection to end distribution to points of use. In the past 20 years of supplying and maintaining systems, we have seen almost everything there is to see with regard to water quality, therefore we will explain why it is important to maintain your system.

Stages of filtration

First stage

Because of the collection process, there is potential for rainwater to carry debris from your roof area. This could be natural elements such as leaves, or manmade elements such as litter. To prevent debris entering the storage tank, a pre-tank filter is fitted to your system to catch any large contaminants before they enter the storage tank. A mesh protection prevents these elements entering the underground tank. Meshing installed in Stormsaver pre-tank filters operate at 1,000 microns, around 1 millimeter in diameter, stopping any larger particles.

Stormsaver have a range of filters, but our most popular underground tank solution is our vortex filter. This is installed within the body of the tank and can be easily accessed for maintenance purposes from ground level. It also ensures the tank only has a 50mm invert level across it, meaning that it doesn’t lower the depth of your tank (which can be more costly to install and maintain). It is important to ensure mesh filters are accessible to service engineers for them to clean on a bi-annual basis. If your filters are not cleaned, a buildup of debris can block the mesh meaning water can pass over the top and just go to drain, wasting your precious free rainwater supply.

Second stage

After rainwater has passed through the crucial pre-tank filter, it will enter the main storage tank via the inlet calmer, where water will remain until it is required. Once there is sufficient demand, water will be extracted through a floating suction filter or fixed foot filter, a component which will rise and fall with varied water levels. This filter floats just below the surface of the water, where the water is the best quality. In line with the British Standard, the floating suction filter will not extract any water from the lower 150mm of the tank. This prevents any excess sediment entering your system. Once your tank is in low level, your system should automatically switch over to mains water.




Third stage

Your rainwater system doesn’t necessarily need a 3rd stage of filtration. However, in situations where occupants are considered vulnerable (health care settings, schools or care homes) or if applications supplied create an aerosol (vehicle wash, irrigation), we would recommend fine filtration.

This stage of the filtration process will differ dependent on the supplier of your system. Stormsaver offer automatic backwash filtration systems which goes down to 35 microns and automatically carries out a backwash every 24 hours. Each backwash lasts approximately 10 seconds.

Our resilient auto backwashing system has been designed to last at least one million uses. This component operates by rainwater passing through a stainless-steel coil to trap any particles. Unlike cotton wound filters (below), these filters are self-cleaning and controlled by a flow meter which communicates when the filter needs to be cleaned. Cleaning takes places through the reversal of water back through the pump which is then disposed of to a drain connection.

Other options include cotton wound filters, as mentioned above, which operate by water passing through layers of cotton to trap any small particles. The micron rating for this part of the system is heavily dependent on the end use, with aerosol usage requiring a smaller rating. These filters need replacing on a regular basis.

The importance of changing cotton wound filters

Our cotton filters are reliable and cost-effective; however, they do require maintenance from in-house maintenance staff. These will require a member of your maintenance team to change the filter on a regular basis, the smaller the micron rating, the higher the frequency of changes.

In our 20 years of experience dealing with rainwater harvesting systems we have often found that in-house maintenance staff have not replaced cotton wound filters frequently. This can compromise water quality as a buildup particle on the filter will prevent clean water getting through. Therefore, if you have opted for this filtration solution it is crucial to ensure these are replaced in line with suppliers’ advice.

UV Disinfection

UV disinfection is optional, but again recommended where water will be distributed in a fine spray, or the occupants are considered vulnerable. This works perfectly with the automatically backwashing filter as it keeps the UV lamp cleaner for longer, preventing any shadowing within the UV system, making it more reliable.


Every electronic or mechanical system will require maintenance to ensure optimum performance and your rainwater harvesting system is no different. Fortunately, Stormsaver systems have the benefit of requiring little maintenance, however it is still important to have a comprehensive plan in place.

We offer robust maintenance packages for any rainwater harvesting system, regardless of supplier. This ensures you have complete piece of mind over water quality. Our experienced servicing team will carry out a full system inspection on a bi-annual basis and offer solutions for any required remedial works.

Stormsaver recommend a tank clean every 2-3 years for the purpose of managing sediment build up in the bottom of the tank. This will assist the floating suction filter with ensuring no sediment enters the system.

British Standard compliance

All of Stormsaver’s filters comply with the requirements set out in BS EN 16941-1:2018 British/ European Standard for Rainwater harvesting. We will be happy to advise you on this.

To enquire about our popular systems or bespoke maintenance packages contact us through



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