Imagine shaking up a glass jar of muddy
water- it is hard for light to shine through the glass because
of all the dirt particles suspended in the water. If you keep
the jar still for a while, however, the dirt particles will settle
out and you will be able to see light coming through the glass.
Turbidity is a measure of how clear
the water is. High turbidity means that there are a lot of particles
suspended in the water and light cannot get through. Low turbidity
means that there are fewer particles in the water and it is more
Turbidity in a stream may increase from:
- soil erosion
- higher levels of algae
- sediment stirred up from the stream bed
Turbidity is measured in nephelometric turbidity units, or NTUs.
Nephelometric simply means how cloudy the water is. The picture
above shows different NTU values for samples of water.
Drinking water must have less than 0.5 NTU, more clear then the
beaker of water shown above with a 10 underneath. Imagine that a
river may have a turbidity of 1500 NTU and must be cleaned to less
than 0.5 NTU in order for people to be able to drink it.