Humic substances are commonly classified on the basis of solubility. The high molecular weight and polyelectrolytic humic substance macromolecules range from a molecular weight of a few hundred for fulvic acid to tens of thousands for the humic acid and humin fractions. Humic substances are excellent chelating agents that bind with and hold metal ions in water, and they also effectively exchange cations with water. Fulvic Acid A water-soluble, natural organic substance of low molecular weight which is derived from humus, often found in surface water. Fulvic acid contributes to the formation of trihalomethanes in chlorinated water supplies, and can contribute to organic fouling of ion exchange resin beds.
True color is distinguished from apparent color by filtering the sample.
True color is mostly found in surface water, although ground water may contain some color if the aquifer flows through a layer of buried vegetation, such as from a long buried slough of a river. Color can be removed by activated carbon filters, sometimes marketed as taste and odor filters. The activated carbon or charcoal must be replaced after a period of time when its capacity for adsorption of the color is exhausted. Another treatment method is coagulation and sedimentation using alum or other chemicals. This process is normally used only in large plants since its complexity requires the care of a trained water treatment plant operator.