The water quality index, which characterizes the intensity of the color of water and is caused by the content of colored compounds; Is expressed in degrees of platinum-cobalt scale. Determined by comparing the color of the test water with the standards. The color of natural waters is due mainly to the presence of humic substances and ferric compounds. The amount of these substances depends on geological conditions, aquifers, the nature of soils, the presence of swamps and peatlands in the river basin, and so on. Sewage from some enterprises can also create a fairly intense color of water.
The color of natural waters varies from units to thousands of degrees. The "true color", due only to dissolved substances, and the "apparent" color caused by the presence of colloidal and suspended particles in the water, the relationships between which are largely determined by the pH value.
The maximum permissible value of chromaticity in waters used for drinking purposes is 35 degrees on a platinum-cobalt scale. In accordance with the requirements for water quality in recreation areas, the color of the water should not be detected visually in a column 10 cm high. The high color of the water worsens its organoleptic properties and has a negative effect due to a sharp decrease in the dissolved oxygen concentration in water, which is spent on oxidizing iron compounds And humic substances.