The primary purpose of these is not to slow down evaporation. In fact they have a negligible effect on the rate of evaporation. Their primary purpose is to abs

The primary purpose of these is not to slow down evaporation. In fact they have a negligible effect on the rate of evaporation. Their primary purpose is to absorb the light spectra that drives chemical reactions in the treated water to prevent carcinogenic bromate from being formed. Most of the reporting on this, including this article, is pretty bad, and causing a lot of laymen to ask questions like yours, because it doesn't make sense as described in the reporting.