Can you please tell me if their any agreement about water quality index in the world?

Question

Can you please tell me if their any agreement about water quality index in the world?

Answer 1

There are specific measurements and analyses used to quantifying water quality depending on how it is to be used.

For drinking water these are turbidity (clarity), microbiological contamination and chemical contamination.  If you were measuring the health, or quality, of a natural water body typical measurements are DO (dissolved oxygen), nutrients (nitrates and phosphates) and clarity.

If want see how many ways there are to quantify water quality go to a technical, or science library, and look up Standard Methods for the Examination of Water and Wastewater

http://www.standardmethods.org/

Answer 2

There are multiple standards, both for different uses (drinking water, industrila, wildlife, agricultural, etc.) and for different agencies. Generally, I've found the standards of the World Health organization to be the most lax.

My own interest is in measuring water quality by using benthic macroinvertebrates and I've been playing around with a manuscript on the subject. It's more than 80 pages long. There are lots of indices that have been proposed.