Turbidity in water is caused by suspended particles or colloidal matter that obstructs
light transmission through the water. It may be caused by inorganic or organic matter
or a combination of the two. Microorganisms (bacteria, viruses and protozoa) are typically
attached to particulates, and removal of turbidity by fi ltration will signifi cantly
reduce microbial contamination in treated water. Turbidity in some groundwater
sources is a consequence of inert clay or chalk particles or the precipitation of nonsoluble
reduced iron and other oxides when water is pumped from anaerobic waters,
whereas turbidity in surface waters may be the result of particulate matter of many
types and is more likely to include attached microorganisms that are a threat to health.
Turbidity in distribution systems can occur as a result of the disturbance of sediments
and biofi lms but is also from the ingress of dirty water from outside the system.