Green technologies for modern settlements with sustainable water and energy management in South Africa.

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The PURAIN Rainwater Filter

Clean rainwater – lowest maintenance expenditure

The PURAIN Rainwater filter, also known as the hydraulic jump filter, is the innovation for roof areas ranging from 60m² to more than 15.000m².

This hydraulic jump technology cleans itself automatically. The design model for PURAIN Rainwater filters comes from nature: At almost every course in a stream, you can see how the hydraulic jump functions. The water flows over one of the stones, smooth and rounded by the action of the water over time. The water flow is substantially changed by the height drop, from a sub-critical to a super- critical flow. At the bottom of the dip, the waterflow changes again to a subcritical flow in a process now commonly known as hydraulic jump. This resulting increase in water power is similar to a strong eddy and any impurities are then forced over the next level and washed away downstream. Finally a filter that is low maintenance and self-cleaning!

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  • Minimal height offset
  • Minimal maintenance intervals 
  • Removing dirt by immersing the sieve 
  • Self-cleaning thanks to the hydraulic jump 
  • Integrated skimmer 
  • Integrated non-return valve 
  • Minimal blocking tendency due to the trapezoidal gap sieve design
  • Filter cleaning efficiency is maintained with the use of the backflushing nozzle. The nozzle flushes the sieve clean from behind
  • Minimal blocking tendency thanks to the division over the total sieve surface 
  • Immediate filtering = no start-up losses 
  • Minimal tilt sensitivity 

The following types of PURAIN Rainwater filters are designed for a variety of needs from domestic to industrial:



PURAIN Rainwater filter for a single family dwelling:  including a non-return valve, protection against small animals entering the tank and skimmer overflow



PURAIN Rainwater filter for a single family dwelling: including a skimmer overflow

PURAIN 150-S and PURAIN 150-200-S

PURAIN rainwater filter incl. skimmer overflow is suitable for wall and tank mounting as well as for ground installation.

PURAIN PR-200 to PR 400

PURAIN PR-150 to PR-400:

PURAIN Rainwater filters for industrial, public or commercial buildings. This series is developed for in tank installation or wall mounting.

PURAIN PR-HD-200 to PR-HD-400

The PURAIN-HD (Heavy Duty) model SLW60 (Heavy duty vehicles up to 60 Tons), is designed as a subsurface variant. PR-HD rainwater water filters are made accessible with conventional manhole lids and rings.

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