Rainwater PreFilters
RAINWATER FILTRATION
Intewa USA – Purain Rainwater Prefilters
Introducing Intewa, manufacturer of the Purain Hydraulic Jump Filter. This hydraulic jump technology cleans itself automatically during a heavy storm. The design inspiration comes from nature: you see it in streams. As water flows over large rocks, a swirling eddy forms at the base. The stones are washed clean by the hydraulic force.
With PURAIN® filters, the inflowing, contaminated water is filtered through an inclined stainless steel trapezoidal sieve and fed into the cistern. The dirt collects in a depression behind the sieve until it is flushed into the overflow by the so-called hydraulic alternating jump during a heavy rain event. In the case of greywater harvesting systems, the filter is automatically flushed free with the aid of a backwash nozzle. In the case of a storage tank overflow, the filter is also cleaned. Due to the unique design, the filters are characterized by the highest efficiency with the lowest maintenance requirements. PURAIN® filters are successfully used in well over 40,000 rainwater and greywater systems worldwide. They are virtually indestructible, require no maintenance components and are therefore particularly sustainable.
The PURAIN filters ensure optimum water quality in your cistern. They are suitable for filtering rainwater fed to a storage tank from roof surfaces* with clay tiles, slate, metal, glass or concrete blocks, or for pre-filtering gray water. The water samples we tested confirm the excellent water quality. The water is perfectly suitable for use in WC, garden, washing machine and many commercial applications.
With rainwater harvesting, a productive source is available in many areas of the world, providing you with free water of excellent quality. The water can be used for garden irrigation, cleaning, flushing toilets, and more.
For over 25 years and in well over 30,000 rainwater harvesting systems, Intewa Purain customers are now collecting the valuable rainwater. We offer an optimal range of filters, plastic and concrete cisterns, pumping and control devices, accessories and complete systems.
See the chart below for sizes and recommended flow rates:
* The "Invert" in the chart above is the drop from inlet to outlet. These are some of the lowest in the industry, and allow for filters to be installed inside tanks, out of sight.
The below ground models are suitable for direct burial, and have an access opening for filter cleaning. ​
Self-Cleaning with 98% Efficiency
Most rainfall is light rainfall — it makes up over 97% of what falls in a typical year. That's why the PR150's design focuses on capturing these smaller events efficiently. Water is channeled into the collection trough, filtered as it passes through, and routed straight into the tank so none of it goes to waste.
- Inlet — stainless steel slotted screen
- Slotted screen
- Collection area
- Filtered water outlet
- Inspection access
Heavy storms are rare but useful. Only 4 to 10 times per year do downpours large enough to trigger self-cleaning occur — and while they only account for roughly 3% of total water collected, the PR150 puts that volume to work. The sudden surge in flow creates a swirling vortex inside the unit, which lifts accumulated debris off the screen and carries it out through the overflow.
- Inlet — stainless steel slotted screen
- Slotted screen
- Jump/vortex zone
- Filtered water outlet
- Debris drain / emergency overflow
- Inspection access
Because heavy rain events flush the screen automatically, the PR150 requires less routine maintenance than comparable filters on the market — and it holds an effective efficiency of 98%, a rare figure for a self-cleaning rainwater filter.
In independent testing, a sample load of 3.5 kg of sand and gravel debris was cleared from the unit in under 30 seconds during a simulated heavy-rain cycle — demonstrating just how effective the self-cleaning action is under real storm conditions.