What NTU rating means water is Turbid?

Question

What is the NTU rating that defines water as being turbid? Or at what rating is the turbidity level too high and dangerous to animals and plants?

Answer 1

I'm not an expert on this subject, but a quick web search led me to this site which could help you further.

Answer 2

What Rajasekaran said about NTU name and measurement is correct.  However the reasons for the measurement vary for different uses of water.

For irrigation water there is no dangerous level.  For plants in water (algae) too much turbidity will block sunlight.  How much is too much, depends on the background or normal level of turbidity in a given body of water.  For example water in a swampy river delta may have a background turbidity of 100 - 200 NTU.  The algae in the water are acclimated to that condition.  Water in a highland lake may have as little as 5 - 10 NTU so the algae in that would be impacted by turbidity if the level rose to 200 NTU.  Rigellian's link has an excellent description about the effects on algae and plankton being affected by turbidity.

Terrestrial animals are fairly immune to issues of turbidity.  There is a point where water is so cloudy that turbidity cannot be measured, but it is still safe for terrestrial animals to drink barring gross microbiological contamination.

Aquatic species are more sensitive.  Because the long term affects of turbidity on algae and plankton this affects the whole food chain in a given body of water.  Again Rigellian's link explains this.

What level is harmful to humans?  The limit in the US is 1 NTU for unfiltered drinking water supplies and 0.5 NTU for filtered drinking water supplies.  These values were determined by laboratory studies, public health studies and statistical analysis as to whether the disinfectants used to purify water do their job.

So it is not the turbidity it’s self that is harmful, it is whether the turbidity interferes with chlorine and ozone disinfection.  In the absence of human pathogens, we could drink the same water as our animal friends.

Answer 3

The full form of NTU is: Nephelometric Turbidity Unit which is a measurement used for expressing turbidity of water. It is measure of light interference and is a function of surface area.

As per Indian Standards, the limit for turbidity upto which water is generally accepted to the consumers is 1 NTU.

However, when the turbidity level is exceeding the above acceptable limit, the water may be tolerated in the absence of an alternate and best source but upto the limit of 10 NTU.

To the best of my knowledge, the turbidity limits prescribed for human consumption holds good for animals also. But in the case of plants, turbidity wouldn't affect plants because plants are with root mechanism sucking only the nutrients they require from the water; but the top soil may get soaked with sediments (causing turbidity in water) in long run affecting the permeability of soil to permit air and water to percolate down to the ground.