Organisms used in water purification

Organisms used in water purification
A flowering water-purifying plant (Iris pseudacorus)

At present, several species of water-purifying plants, bacteria, and fish are used in water purification, improving efficiency and/or ecosystem support.



Plants perform multiple roles in water purification. They provide shade, a refuge for fish, oxygen for aerobic bacteria.[1] In addition, fish can limit pests such as mosquitoes.

The choice of organism depends on the local climate different species and other factors. Indigenous species usually tend to be better adapted to the local environment.


A water-purifying plant (Iris pseudacorus) in growth after winter (leaves die at that time of year)

Different plant species are necessary in each of four depth-zones.[2]

  • 0–20 centimetres (0–7.9 in)
  • 40–60 centimetres (16–24 in)
  • 60–120 centimetres (24–47 in)
  • Greater than 120 centimeters (47 in)

Water purifying

Plants purify water by consuming excess nutrients and by de-acidifying it by removing carbon dioxide.


  • Stratiotes aloides, for temperate climates, depth 40-60cm, is one of the best options.
  • Hydrocharis morsus-ranae, temperate climates, depth 40-60cm is one of the best options. Extremely invasive and is listed on the Washington State Noxious Weeds list.
  • Acorus calamus, for temperate climates



Different species required for each of 3 depth-zones. The fish need to be herbivores.

  • Surface
  • Middle
  • Bottom


  • Leuciscus leuciscus, for temperate climates.
  • Leuciscus idus, for temperate climates.
  • Scardinius erythrophthalmus, for temperate climates.


  • Rutilus rutilus, for temperate climates.


  • Tinca tinca, for temperate climates.


Indigenous bacteria are preferred to ensure that good adaptation to local conditions. Bacteria can be grown by submerging straw (or other plant material) in water for several days. The bacteria automatically populate the material.

Extra considerations

For ecologic/self-purifying ponds, de-nutrified soil needs to be taken for the plants to prevent the possible growth of algae. Coconut fibre growing medium is best used to prevent soil from being spread around and to sometimes to let the plants root in.

Example system

The following choices occupy all depth-zone niches and are mutually compatible in the same pond.



  • Surface—Leuciscus leuciscus, Scardinius erythrophthalmus, ...
  • Middle—Rutilus rutilus
  • Bottom—Tinca tinca

See also


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