Turbidity

Subject: Environment

Context: Debris and silt across Ganga after Uttarakhand flood raised turbidity of water impacting water supply in Delhi.

Concept:

It is the degree to which the water loses its transparency due to the presence of suspended particulates. It is considered good measure of quality of water.
Turbidity is a measure of relative clarity of a liquid and is measured in Nephelometric Turbidity Units (NTU). Debris, silt and mud in the water are among the reasons behind high turbidity.
WHO establishes that the turbidity of drinking water shouldn’t be more than 5 NTU, and should ideally be below 1 NTU.
A turbidity measurement could be used to provide an estimation of the TSS (Total Suspended Solids) concentration, which is otherwise a tedious and difficult parameter to measure.

Sources/Factors of turbidity include:

Phytoplankton
Sediments from erosion
Resuspended sediments from the bottom (frequently stir up by bottom feeders like carp)
Waste discharge
Algae growth
Urban runoff

Impact of turbidity

Affects drinking water quality
Suspended particles absorb heat from the sunlight, making turbid waters become warmer, and so reducing the concentration of oxygen in the water
Many organisms can’t survive in warm water
It also helps the attachment of heavy metals and many other toxic organic compounds and pesticides