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The PURAIN filter series for rainwater and greywater harvesting

We produce the patented PURAIN filters from DN100 to DN400 connection width for installation inside a cistern, in the ground or free-standing.

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.

  • self-cleaning due to alternating spring effect
  • minimal height offset
  • minimum maintenance intervals
  • loosening of the dirt by immersion of the screen
  • integrated skimmer for PR100 to PR150
  • integrated backwater flap for PR100
  • minimal tendency to block due to trapezoidal slotted screen
  • low sensitivity to inclination

Best water quality

The PURAIN rainwater filter ensures optimum water quality. PURAIN rainwater filters are designed for filtering rainwater fed to a storage tank from roof surfaces with clay tiles, slate, metal, glass or concrete blocks.

  • Self-cleaning due to alternating jump
  • The indestructible stainless steel slotted screen
  • The integrated overflow skimmer
  • Optimal cleaning effect due to backwash nozzle

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Traffic loads up to SLW60

As an in-ground variant, the PURAIN HD is designed for heavy-duty trucks up to 60 tons. Standard manhole covers and rings are used to make the PR-HD rainwater filters accessible.


Self-cleaning with 98% efficiency

Thanks to the technology of the alternating jump principle, the filters clean themselves. Nature provided the model for the PURAIN rainwater filter: You can see how the alternating jump works at almost every stream. The water flows over a stone rounded by the current. When it hits the depression, a flow vortex is then created, which is called the alternating jump. The energy of the water then carries light and heavy particles back up over the next step and then further downstream.

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Assembly, installation and maintenance-friendly

Due to the self-cleaning by the alternating jump and the slotted screen design, the filter is extremely low maintenance compared to all other self-cleaning rainwater filters. The PURAIN rainwater filters have standardized DN socket or spigot end connections for easy cistern installation.

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PURAIN product series

Tailored to your needs, many standard PURAIN filter types are available for your object. We also manufacture special sizes and connection widths on request.

Good to know

Dimensioning information

The PURAIN rainwater filters are usually dimensioned simply on the basis of the diameter of the connected rainwater collection line.*

If the diameter of the planned collection pipe is still unknown, the following table can be used as a guide. It gives an overview of the dimensioning of these rainwater connection pipes according to DIN 1986 at a design rainfall rate of r = 300 l/sha and a gradient of 1.5 %. The runoff coefficient indicates the factor by which the rainfall runoff volume can be reduced as a result of the roof type.

  • Runoff coefficient 1,0 = theoretical value
  • Runoff coefficient 0.8 = sloped hard roof
  • Runoff coefficient 0.5 = extensive green roof

*The dimensioning of the greywater collection pipes for the use of the filter in greywater recycling systems can be found in the INTEWA Wiki.



Flow rate (l/s)
at 1.5% slope DIN1986


Runoff coefficient m²

For rainwater harvesting, PURAIN filters can be installed in most common cisterns, such as plastic, concrete, indoor and outdoor storage tanks. Many dealers deliver their tanks with PURAIN filters already installed. The PURAIN filters are also suitable for installation outside the cistern, if required. The PURAIN 150 and PURAIN HD filters are designed for direct buried installation. When installing the PURAIN filter, make sure that there is a height offset, even if small, between the inlet and outlet. For heavy rainfall areas and for greywater recycling systems, the PURAIN filters without weir are used in the type M design.

The PURAIN filters operate with minimum possible height offset between inlet and outlet. In a self-cleaning filter, such a height offset and the alternating jump principle are the only way for perfect operation. For very simple rainwater harvesting systems for garden irrigation and lower demands on water quality, we offer the collecting filter basket and the PLURAFIT filter with various inserts without height offset. These filters are particularly suitable for retrofitting rainwater harvesting systems for garden irrigation where no height offset is possible.


Get an overview of the numerous applications of the PURAIN filter.

In our own Online-Store you will find detailed product information.

Here you will find brochures, instructions, certificates, technical drawings and much more.

Dimensioning of INTEWA products

Planning sheets for various applications

Rainplaner software

With our knowledge portal we offer you information about stormwater management, water reuse and more.