Tannins are a natural organic material that can be associated as by-products of nature’s fermentation process, being created as water passes through marshy soil and decaying vegetation.  This can cause your water supply to have a color ranging from faint yellow to dark tea-like coloring often accompanying an earthy or musty odor.    Tannins are most common in surface water supplies and shallow wells rather than deep wells.  Coastal areas containing large marshy, low-lying lands are the most susceptible to tannins.


Tannins are normally found in surface water supplies such as lakes or river sources, and shallow wells especially ones located near low-lying, marshy areas.  Coastal, swampy regions are highly susceptible to tannins mas well.


A simple and easy process to test for tannins would involve filling a clear glass with water and letting it sit overnight.  If the color settles to the bottom of the glass, the discoloration is most likely iron and/or manganese and probably not tannins.  But if the intensity of the color remains intact and seems to stay suspended in the water sample, it may very well be tannins.   A certified lab would be able to take a sample from there and inform you of what tannins are present, if any.

It would also be a good approach to test for sulfates, iron, alkalinity, hardness, and total dissolved hardness (TDS) as well.  These contaminants can help to determine which treatment method(s) will be most effective for your situation.  It is also wise to rule out iron from the scenario since iron can create a false positive for the presence of tannins.  Having iron content removed from the results can help to determine the true tannin concentration.


Tannins will make your water unappealing to drink and unaesthetically pleasing to be seen.  It may stain your toilets, tub, and laundry, but besides the stress those things may add to your life, tannins present no hazard to your health.  It is a good indicator that your water could be coming from surface water, meaning that this may be a good path for pathogens to enter your drinking system as well which could be extremely harmful to your health.


Tannins are traditionally removed using ANION EXCHANGE RESIN.  This resin type is sensitive to hardness and generally requires pretreatment with a softener. A softener would extend the life of the resin helping to increase tannin absorption.   Anion resins also tend to lower the pH of your water calling for a neutralizer to be installed at the end of the water treatment system.   A large issue with having other treatment in front of tannin removal is the effects the tannins may have on that equipment.   Tannins going through filters not intended to remove tannins can become coated and not filter and/or exchange the way the media was intended to do.

Oxidation and filtration is another common method to remove tannins, but is more complex than anion exchange softening.

BWS offers some greener solutions for tannin removal with our ULTRAFILTRATION SERIES

REVERSE OSMOSIS is another effective method for removing tannins. Since tannins are high molecular weight organics RO should reject them effectively. However, tannins will tend to foul the membrane in the system. It also is very expensive to properly install a whole house RO system to treat all of the water