What is considered good, moderate & bad levels of turbidity (NTU) in a river?

Question

What is considered good, moderate & bad levels of turbidity (NTU) in a river?

Answer 1

I'm no expert, I've only had to measure turbidiy once for an experiment, but Googling around gave me some ideas.

I've seen "safe level" of drinking waters anywhere from 0.5-5NTU. Now, I'm going to assume you mean a freshwater river not near some city or something, so should be clean and (relavively) drinkable.

I'd say the 1NTU would be a good level for any river, when you get around 5NTU it's getting a little dirty, and when you get 7.5+ the river isn't good. However, I would suspect at 7.5 NTU the river might not look very bad, in fact it might look quite normal, but it wouldn't be good to drink.

Answer 2

A good NTU level for a river would be under 50 NTU.

Moderate would be around 50 NTU-120 NTU.

Bad would be 200 or above.

It should be noted that any NTU values under 20 cannot be seen reliably with the unaided human eye.

Drinking water standards in the US are regulated by the EPA and they have to .3 NTU or under. There is no such thing as NTU free water....even distilled water. I have personally treated river water out of the Red River of the North on the Minnesota/North Dakota border during spring runoff in excess of 500 NTU.