What NTU rating means water is Turbid?
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
