Water quality is an important factor in the health of your tank, but an even greater factor in a town's ponds and lakes. A city with bad water risks its inhabitants getting sick, and failure of crops and livestock in the surrounding area. It's important to know how water is assessed though, and the steps taken in doing so. The first step in assessing water quality in a lake should be just a general scan of the lake, is there any clearly visible source of pollution, does it look like there are chemical spilled in the water and how much litter is around the lake. Along with that water samples should be taken to test the ph levels and algae counts. Doing this is a relatively cheap way of doing a general test of the water with out paying money for chemical panels, which are more expensive. If the water does look like its polluted, and the ph test are coming back off, and the count of algae is showing low diversity it is time for the chemical panels. You will need to know exactly what is wrong with your water source in order to fix it, this accuracy is most easily achieved through specific chemical tests.

Signed, Ahab