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Tannins are a natural organic material that can be the byproducts of nature’s fermentation process, be created as water passes through peaty soil and decaying vegetation, such as leaves, grasses, pine needles, and other organic matter. This can cause water to have a faint yellow to tea-like color, and can cause yellow staining on fabrics, fixtures, china and laundry.
Tannins may give a tangy or tart aftertaste to water. They may also cause water to have a musty or earthy odor. Tannins – also known as fulvic or humic acid – are more common in surface water supplies and shallow wells than in deep wells. Water in marshy, low-lying, or coastal areas is also more susceptible to tannins.
A simple test for tannins involves 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 caused by iron and/or manganese and not tannins. If the intensity of the color remains intact, it most likely caused by tannins.
