Temperature also can affect the ability of water to hold oxygen as well as the ability of organisms to resist certain pollutants. The range goes from 0 - 14, with 7 being neutral. Water that has more free hydrogen ions is acidic, whereas water that has more free hydroxyl ions is basic. Since pH can be affected by chemicals in the water, pH is an important indicator of water that is changing chemically. Water with a pH of 5 is ten times more acidic than water having a pH of six.
Pollution can change a water's pH, which in turn can harm animals and plants living in the water.
Specific conductance is a measure of the ability of water to conduct an electrical current. Pure water, such as distilled water, will have a very low specific conductance, and sea water will have a high specific conductance. Rainwater often dissolves airborne gasses and airborne dust while it is in the air, and thus often has a higher specific conductance than distilled water. Specific conductance is an important water-quality measurement because it gives a good idea of the amount of dissolved material in the water. Probably in school you've done the experiment where you hook up a battery to a light bulb and run two wires from the battery into a beaker of water.