Color in water caused by Tannin
Tannin? Something new? No, but certainly a recent addition to water treatment technology.
CONSUMER REPORTS WATER SOFTENERS
For many decades an effective treatment for Tannin has eluded water treatment specialists. With many common characteristics similar to its opposite, iron, Tannin is commonly mistaken for iron. It always shows itself as color in the water and often causes staining, especially on clothing. The only visible means of telling the difference between Tannin and iron is the type of stain found on clothing. Tannin leaves splotches of stains, often in the middle of a shirt or bedding. Iron generally stains uniformly throughout the whole garment and shows a preference for seams, folds and collars. If your towel has a splotch of stain, or two, almost appearing like a spill on the towel or shirt, you could easily be dealing with Tannin. So what is it?
Tannin is the color left in water from the leaching of color from organic matter. A tea bag is a Tannin bag. Dip a tea bag in water and you have color and taste. Spill it on your shirt and you have a tannin stain. Tannin is most often caused by decaying organic matter in the water table. Or when the water is drawn from a surface source such as a lake or river, it is caused by dead leaves and trees in the water. Low hanging branches will leach color into the water. In my area of North America, Cedar trees are a major source of Tannin. The dead needles from a Cedar tree turn brown and cause much color in lakes and shallow wells.
Tannin has the opposite ionic charge from its co-conspirator, iron. Iron caused by inorganic substance has a "plus" charge where as Tannin, caused by organics has a "minus" charge. Therefore, although it is easily mistaken for iron, it is not removed by an iron filter.
The most common system for Tannin removal is an anion filter media. This porous media adsorbs the Tannin onto the resin, and is then backwashed with sodium chloride. The system functions very much like a water softener but is opposite in charge. It also uses much more salt than a water softener and the resin bed has a finite life expectancy of 3-5 years, if cleaned regularly. Whereas efficiency can be sought after in a water softener, such luxury is not advised in a Tannin filter. You must dump the salt to it to keep the resin clean or it will saturate and need replacing. The resin is much more expensive than a softener resin.
Another possible agent for Tannin control is an oxidizing agent such as chlorine, ozone, or hydrogen peroxide. But each of these needs to be tested on the subject water to determine which will have the best effect. Ozone or peroxide are my personal choices over chlorine for health and environmental reasons, but the final decision needs to be based on the test results of a laboratory test application. Of course the anion filter will always remove the tannin but then the amount of salt needed can be the detriment to the application.
Tannin will show up positive on an iron test. This makes assumptions regarding iron in your water very hazardous to successful treatment applications. Unlike iron, in which the oxidizing agent precipitates the iron into a particle to be filtered out, Tannin is bleached out. The trial run is to take a liter of the water in a white bowl, put 3 drops of chlorine in the liter of water, and sit back and watch. If the water bleaches clear after a few minutes (5-20 minutes) the color is tannin. If the water goes darker, or if you can visibly detect particles in the water that were not there previously, the color is caused by iron. In any geographical area where Tannin is a possibility this test should always be performed.
When dealing with chemical treatment of water problems, remember two rules of thumb.
1. Contact time is critical. The longer the contact time of the water with the chemical, the better the results.
2. Remove the chemical before sending the water throughout your home. Some chemicals are toxic to ingest of course, but some are even toxic to breath the fumes.
My personal preference when removing Tannin from household water, is the anion filter media. The large amounts of salt needed to regenerate the system will require a separate sump hole to be dug in the ground where the regenerate can be disposed of. I believe this should be done for water softeners too. Salt is very bad for septic systems, and even municipal water treatment systems are better off without this bacteria killing agent which deplete the systems ability to treat water and it also corrodes cement holding tanks.
Unfortunately, as we move into the more complex problems which can present themselves in water, there are no magic solutions. You have to look at the available technologies and decide which applications will achieve the desired result. What is the capital cost, the environmental cost, the maintenance cost? How much room will it take up in your home? Also, you must deal with a reputable water treatment dealer and obtain as much assurance from the dealer as possible regarding the outcome of the recommended treatment. Please, do not be enticed by price cutting on the part of over zealous sales people. Complex water may require expensive complex solutions. Sorry!
Water Color - Tannin CONSUMER REPORTS WATER SOFTENERS
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