What issue do colloidal substances primarily cause in water?

Colloidal substances primarily cause turbidity in water because they consist of very small particles that remain suspended and do not settle out easily. These particles can scatter light, which is why water containing colloids appears cloudy or murky. Turbidity is an important water quality parameter, as it can affect the aesthetic quality of water and can be indicative of the presence of other pollutants or pathogens.

Unlike corrosion, which involves the degradation of materials, or hardness, which refers to the concentration of calcium and magnesium ions in water, turbidity specifically relates to the presence of suspended particulate matter. Filtration processes are often required to remove colloidal substances from water to achieve clear water quality. Therefore, the primary issue caused by colloidal substances in water is indeed turbidity.