Samantha009 emailed us a very direct question:

What are tannins and what effect do they have on my drinking water?

Tannins occur in nature as organic matter and typically get created as water passes through peaty soil and/or decaying vegetation. They normally have a faint yellow to tea-like color, and can cause yellow staining on fabrics, fixtures,
china and laundry.

As far as detecting tannins (without a test kit), one can sometimes detect them in water as a tangy or tart aftertaste. Some people have also attributed a musty or earthy odor in their water to tannins.

Other names for tannins: fulvic acid or humic acid.

Because of the ways in which tannins get created, you will more likely find them surface water supplies and
shallow wells than in deep wells. Water in marshy, low-lying, or coastal areas also plays host to tannins quite frequently.

With regard to health effects of tannins in drinking water, they pose more of an aesthetic problem than a health risk. They may make water unappealing to the palate and can cause stains in laundry… but at this time most health experts agree that they present little or no health hazard.