Frequently asked questions and answers

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Where can I install the PURAIN rainwater filter?

The INTEWA PURAIN filters can be easily installed in most standard tanks of  plastic, concrete, indoor and outdoor construction. Many distributors deliver your storage tank already fitted with a PURAIN filter. The PURAIN Filter is also suitable for installation outside the tank if required. HD Filters are designed for direct subsurface installation. While installing the PURAIN filter, make sure that a lower height offset is present between the inflow and the outflow.

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How much roof area can I filter with a PURAIN rainwater filter?

We offer PURAIN rain water filters in five sizes: DN100, DN150, DN200, DN300, DN400. The roof area that these filters cover ranges from between 60 m² and 15.000 m². The selection of a suitable filter critically depends on the installed inflow diameter of the collecting pipe. For example, if the DN100 is installed as a collecting pipe, then the PURAIN PR 100 should be used.

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Is there a filter without height offset between inflow and outflow?

The PURAIN rainwater filter works with the minimum possible height offset between the inflow and outflow. A height offset is a prerequisite for a self-cleaning filter in order to ensure proper operation. Since 1993, INTEWA has accumulated a lot of experience testing different types of self-cleaning filters – none of which, function with a high degree of efficiency. Alternatively, only a collection filter may be used in place of a hydraulic jump, however they have to be cleaned regularly and do not guarantee the best quality water filtering.  

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Is the rainwater filtered by PURAIN well suited for washing machines?

The water filtered by the hydraulic jump filter is perfectly suited for use in toilets, washing machines etc. It should be noted that the quality of water also depends on the storage of the rainwater. Factors, such as temperature of the storage tank, inflow calmer, overflow skimmer,  size of tank, etc. are critical for an optimum quality of water.

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Does self cleaning = maintenance free?

The PURAIN-filter is extremely low maintenance. Dirt and leaves in the sedimentation chamber do not need to be removed because they will be flushed away with the next heavy rainfall. If the sieve does become clogged, it is easily cleaned through the tank lid with a high pressure cleaner. Alternatively, in rare cases, the sieve can be removed for cleaning. Should a filter be mounted in a hard to access place, it can also be cleaned via the installation  of a backflushing nozzle. This is available as a PURAIN accessory. We recommend that you check your filter about sieve twice a year.

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How is the efficiency in other conditions of rain?

The overall efficiency of the PURAIN rain water filter is rated at 98 %. Hereby, the small to medium rainfalls are collected 100 %, but the heavy rains (which account for only about 3 % of annual rainfall yield), are utilized for the self-cleaning function of the hydraulic jump filter. Even in areas which experience more heavy rainfalls the efficiency of the PURAIN filter is well over 95 %.

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How do I install the non-return valve and overflow skimmer used with the bigger PURAIN rainwater filters?

The non-return valve and overflow skimmer, made from moulded parts, are separately installed in the tank along with the bigger PURAIN rainwater filters PR 150 to PR 400.


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