Cistern filters can filter coarser and finer


The rainwater itself is clean enough to be safely used as a useful water for washing machines and toilet flushes, for example. However, it often flushes leaves, sand, plant parts and other dirt particles on the way to the cistern. There are special cistern filters for this, which can be installed at different points in the rainwater harvesting system.

Passage and basket filters

From a technical point of view, cistern filters work according to two basic principles. They serve as a dirt separator when water flows through, or they collect the transported dirt particles from the rainwater in a filter basket. Often the filtering effect is increased by the combination of both techniques.

If the rain water from the cistern in the garden is only used for watering the plants, simple coarse filtration is sufficient. Through a mesh or sieve insert, which can be built as a rainwater filter itself, leaves, petals, fruit and plant parts are collected.

Placement and filter units

In the case of using the cistern water as utility water with connected installation for toilet flushing or washing machines, a more thorough filtering must be carried out. If the cistern is connected to a domestic waterworks, even fine sand and sludge particles must be minimized.

Cistern filters can be placed in different places of the cistern and their piping. In addition to a rainwater filter in the inlet nozzle or in the downpipe, filter units are common in the cistern itself. For underground installation special earth filters provide good services, the advantage of which is easy accessibility and cleaning.

Filter types and function types

The typical filter groups are divided into:

  • Downpipe and nozzle filter
  • earth filter
  • cistern filter
  • industrial filters

These types are subdivided according to their technical function type:

  • Rainwater collector
  • cartridge filters
  • strainer
  • basket filter
  • Syphonfilter
  • volume filter
  • infiltration filter
  • retention filter
  • Double chamber filter
  • Leaf Separator

Common filter combinations

If an at least two-stage cistern filter is required, as is absolutely necessary for a domestic water supply with utility water transfer, a coarse and a fine filter system are usually used together. Typical combinations are:

  • Rain collector and basket filter
  • Leaf decanters and siphon filters
  • Volume filter and sieve filter
  • Rain collector and cartridge filter

The decisive factor is the removal of coarse dirt particles such as leaves, branches or fruit from the fine filtration, which is intended to hold back by narrow-meshed pores, especially sandy and muddy dirt.

Clean and maintain the filter

Since the costs for cleaning the cistern can be considerable, cistern filters should extend the necessary cleaning cycles as far as possible. Therefore, easily accessible types of filters whose inserts such as screens or baskets can be cleaned easily and often are advantageous.

If the rainwater flow, for example, in summer for a long time to fail, a regular flushing the cistern filters is recommended. This also prevents the cistern from starting to stink, which can be caused for example by moisture residues. In mechanically filtered rainwater are always organic residues that lead to the formation of brackish water and the associated stench.

Tips & Tricks

If the construction of their cistern allows it, intermediate filters with their own settling chambers increase the cleaning effect of small particles.


Video Board: 3P Technik UK Zisternen Filter