If water contains suspended particles or colloids, transparency is reduced. This is due to light scattering caused by these particles. Photometric turbidity measurement is used to determine how high the proportion of undissolved particles is in the water sample. Particles are undesirable in water for aesthetic and hygienic reasons. Algae, bacteria, rust particles, soil particles, lime particles contribute to the increase of the turbidity value.
In well systems, higher levels of manganese and iron often lead to increased turbidity. Cleanest water has a turbidity of 0.016 NTU, good drinking water 0.05 - 0.5 NTU. The limit value of the drinking water regulation is 1.0 NTU, because clean drinking water should be free of undissolved substances. If the turbidity is high, deposits can form in the piping system and odor and taste problems can occur. In addition, bacteria can attach to solid particles or settle in microflocs. Keeping turbid water hygienically perfect is therefore difficult.