The entire question of water quality, allocation, use, and conservation is one of the most significant issues today's children will face in their lifetime. To compound the problem, water that appears clean and pure often isn't, and water that appears cloudy and dirty can be fit for human consumption. Water that is fit to drink is called potable. Clean water is also free from significant amounts of heavy metal contaminants such as lead, mercury, and cadmium. Once thought to be insoluble, such organic chelates as methylmercury can be dissolved in water and are fat soluble in the higher animals such as birds, fish, and man.
Heavy metals damage the liver, kidneys, and reproductive organs as well as being carcinogenic.
Clean water also has an appreciable amount of dissolved oxygen which helps the water keep itself clean and improves the taste. Bacterial culture tests take several days and may not be practical if great distances are involved between the school and the local USGS office. A sterilized screw top bottle for each student, a copy of the USGS Data Source book for comparative purposes. Prior to this visit, discuss with the class the issues associated with water quality and the three major aspects of water quality described above. The day before the visit pass out the sterilized bottles and explain how to collect water samples.