The pH value of water, on a scale of 0 to 14, measures the concentration of hydrogen ions. Pure distilled water is considered neutral, with a pH reading of 7. For every one unit change in pH there is approximately a ten-fold change in how acidic or basic the sample is. Very acidic lakes and streams cause leaching of heavy metals into the water. Carbonaceous biochemical oxygen demand measures the amount of organic material in the water.
Organic material is fed upon by aerobic bacteria which require oxygen.
In this process, organic matter is broken down and oxidized. Protozoa prey upon the growing population of bacteria and also require oxygen. CBOD is a measure of the quantity of oxygen used by these microorganisms in the aerobic oxidation of organic matter. Many of the physical, biological and chemical characteristics of surface water are dependent on temperature. Conductivity measures the electrical conductants in the water.