Metro Vancouver tests and analyzes more than 25,000 drinking water samples every year. One reason we test is for cloudiness, or turbidity. Cloudy water is created when fine particles like sediment or organic matter wind up in the reservoirs through heavy rainfall. Other causes of turbidity can be construction, system operational changes, high water flows due to a fire or flusher truck filling, or high flows due to hot weather.
Turbidity is measured in units called nephelometric turbidity units (NTUs), and is monitored both by a built-in monitoring system at the water supply intakes and by daily laboratory tests. Increased turbidity in drinking water may interfere with disinfection. So, as turbidity increases there is the potential for an increase in gastrointestinal illness.
Turbidity levels above 1 NTU prompt increased disinfection levels as a safety precaution and may prompt Metro Vancouver to change the operation of the system to maintain water quality. People with compromised immune systems should always use drinking water that has been boiled or treated to the same level as boiling.