Turbidity is the cloudiness caused by fine suspended matter in the water. It affects the appearance of water. The main contributors to turbidity in water are clay, silt, fine organic matter and microscopic organisms, such as algae.
There are four main concerns when dealing with turbidity in water:
- Suspended solids are an excellent base for bacteria growth.
- Harmful pollutants such as heavy metals and pesticides are easily absorbed by suspended solids.
- Suspended solids represent a risk for the main water distribution systems, pumps and other equipment where tend to deposit and block pipes and nozzles. Deposits on heat-exchange elements hamper heat transmission.
- Turbidity has an impact on the aesthetic acceptability of water. Consumers relate the appearance of water to its safety and turbid or coloured water is considered unsafe to drink.
Turbidity impact on bacteria growth and disinfection effectiveness
Suspended particles in water act as a protective shield for micro-organisms and provide an excellent substrate for bacteria growth. In general turbidity should be kept below 1 NTU for effective disinfection. The lower the turbidity of the water at the time of chlorination the more effective chlorination will be and if chlorination occurs at turbidities higher than 1 NTU, the effectiveness of the chlorination process should be validated.
Turbidity impact on pipes and equipment
The major problem with turbid water is that the matter it contains can remain in suspension for a long time. This is particularly true for colloidal suspended solids (< 1 μm ) that can stain clothes, foster corrosion in plumbing fittings, block irrigation spray nozzles, contribute to a build-up of sludge in drippers and pipes and reduce the efficiency of water-softening units.
Reference values for turbidity in water
According to the Australian Drinking Water Guidelines are:
- < 5 NTU is not noticeable in a glass
- < 0.2 NTU is the target for effective filtration of Cryptosporidium and Giardia
- < 1 NTU is the target for effective disinfection
Particles smaller than 1 μm as they do not scatter light and are thus, not detected using turbidity measurements.