What it is:

  • Tannins are an aggregation of not specifically defined natural organic material included in total organic carbon that are byproducts of degradation of vegetation.
  • Through this process tannins can cause water to look yellow to brown and cause stains on fabrics, china, laundry and fixtures.
  • They can cause water to have a tangy or tarty aftertaste and cause a musty odor that can come from decayed vegetation or animal matter.
  • Tannins can also include fulvic or humic acids.
  • There are around 12,000 types of tannins and most people drink them every day through either tea or coffee.

Occurrence:

  • Tannins most commonly occur in surface water supplies or shallow groundwater.
  • We consume tannins in our diets on a daily basis, including in tea or coffee drinks.
  • They occur in almost any body of water where large quantities of vegetation have been decaying.

Health effects:

  • Tannins are an aesthetic contaminant, meaning they don't cause any potential health risk per se.
  • The contaminant does leave water looking unpleasant and can cause your water to smell bad.
  • These chemicals are the principle contributors to TOC that produces disinfection by-products. Some of those are regulated and pose potential health risk concerns.

Water treatment:

  • Using an anion exchange resin in cases where tannins register above a pH of 6 is the main way known to treat for tannins.
  • Conventional water treatment involving coagulation and oxidation are the common ways that tannins and TOC are managed in public water systems.
  • Cation exchange water softeners can be used as pretreatment for tannins in drinking water. The softener will extend the life of the anion resin by eliminating the water hardness.
  • One way to help remove the color caused by tannins is to use an ultrafiltration system.
  • Below a pH of 5, it is best to use activated carbon to treat for tannins.

Regulation:

  • There are no current regulations for tannins at this time as they cause no real health threat, but they are significant contributors to TOC that generate disinfection byproducts. There are TOC reduction requirements in the surface water filtration rules.

Sources: Water Systems Council, Safe Water Technologies Inc., Clean Water Store, Alpha Water Systems Inc.