Water Quality - Rollover numbers to get an idea of the pH scale

Water quality assessments require the determination of a variety of factors; pH, suspended solids, bacterial counts, and chemical pollutants. The acidity of water is indicated by using the pH scale. The scale ranges from 0 (maximum acidity) to 14 (maximum alkalinity) with a neutral point of 7 in the middle. Adding acid causes the value to approach 0. The pH scale is a negative logarithmic scale and a difference of one pH unit represents a 10 fold shift in hydrogen ion concentration. For example, a pH of 3 is 10 times more acidic than a pH of 4 and 100 times more acidic than 5. The greater the hydrogen ion concentration, the lower the pH and the more acidic the water. Normal rain has a pH of 5.6, slightly acidic because of carbon dioxide picked up in the earth's atmosphere by the rain.

Different instruments are used to measure different chemicals in the water; a gas chromatograph-mass spectrometer is used to analyze pesticides, PCBs and other organic compounds, while a plasma emission spectrometer is used to analyze metals. Today's instruments are able to detect more substances and in smaller quantities, thanks to technological advancements. Instruments can now detect levels as low as one part per trillion of some substances - the equivalent of detecting one thousandth of a teaspoon of salt dissolved in an Olympic-size swimming pool!

The quality of water can also be determined using bacteriological criteria. Several kinds of bacteria are used as indicators to diagnose fecal contamination of water. Many swimming beaches are closed if the bacterial count exceeds government standards to protect the public from developing diseases. Escherichia coli and Salmonella are two common indicators of human waste and fecal contamination.

In addition to these methods, water quality is often assessed by the amount of suspended inorganic particles or solids in the water column, called the turbidity. These substances are usually consist of organic detritus or alluvium (rocky debris consisting of clay, silt, and small pebbles). The more turbid the water, the less sunlight travels through the water column and the less there is for aquatic plants to perform photosynthesis. These suspended particles can also clog the gills of fish and crustaceans, thereby interfering with respiration.

http://www.aquatic.uoguelph.ca/