What We Mean by Water Purification

When we refer to water purification, it makes little sense to discuss the subject without first identifying the contaminants that we wish to remove from water. Also, the source of the water is of importance. Our discussion at this point focuses on drinking water. Groundwater sources are of a particular concern, because there are many communities throughout the U.S. that rely on this form. The following are some of the major contaminants that are of concern in water purification applications, as applied to drinking water sources, derived from groundwater. 

Heavy Metals - Heavy metals represent problems in terms of groundwater pollution. The best way to identify their presence is by a lab test of the water or by contacting county health departments. There are concerns of chronic exposure to low levels of heavy metals in drinking water. 

Turbidity - Turbidity refers to suspended solids, i.e. muddy water, is very turbid. Turbidity is undesirable for three reasons  

Bacteria are smaller than protozoa and are responsible for many diseases, such as typhoid fever, cholera, diarrhea, and dysentery. Pathogenic bacteria range in size from 0.2 to 0.6 /tm, and a 0.2 /tm filter is necessary to prevent transmission. Contamination of water supplies by bacteria is blamed for the cholera epidemics, which devastate undeveloped countries from time to time. Even in the U.S., E. coli is frequently found to contaminated water supplies. Fortunately, E. coli is relatively harmless as pathogens go, and the problem isn t so much with E. coli found, but the fear that other bacteria may have contaminated the water as well. Never the less, dehydration from diarrhea caused by E. coli has resulted in fatalities. 

Viruses are the 2nd most problematic pathogen, behind protozoa. As with protozoa, most waterborne viral diseases don t present a lethal hazard to a healthy adult. Waterborne pathogenic viruses range in size from 0.020-0.030 jtim, and are too small to be filtered out by a mechanical filter. All waterborne enteric viruses affecting humans occur solely in humans, thus animal waste doesn t present much of a viral threat. At the present viruses don t present a major hazard to people drinking surface water in the U.S., but this could change in a survival situation as the level of human sanitation is reduced. Viruses do tend to show up even in remote areas, so a case can be made for eliminating them now. 

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