Many water supplies drawing water from swamps or similar surface water (e.g. Everglades) may contain Tannin. Tannin is harmless but colors the pool with a greenish tinge. More annoying, it reacts with oxidants (like chlorine) in the water to form various reaction by-products, which are irritants to eyes and mucous membranes and cause dry skin as well as brittle hair.
The WAPOTEC solution: