What are Tannins?

Tannins are a group of organic acids, the most common of which are Humic and Fulvic acids. Tannins are produced in plants, the bitter taste discourages predation. They are also what gives tea its characteristic brown colour

In water, tannins are more of a nuisance than harmful as they lower pH and discolour water.

How do tannins get into my water?

Tannins are common in both surface and ground waters. Surface waters which flow through large amounts of decaying vegetation will contain tannins.

In groundwater peaty and marshy areas have capacity to leach tannins into water.

What do tannins do?

The simplest issue is that discoloured water is not palatable and can cause staining.

However there are a few associated issues:

  • tannins affect clarity of water and are easily oxidised and thus affect common disinfection methods( like UV and chlorination)
  • water containing tannins has a food source for bacteria creating a higher risk
  • tannins can bind with iron making it harder to remove
  • Being acids, tannins can lower pH of water, which may need correction

How can I remove tannins from my water supply?

There are a few methods to remove tannin, which one is suitable will depend on the amount and related water chemistry.

Some common methods are:

  • activated carbon
  • oxidation/filtration
  • organic scavenging anion resin