Ground-water...how good it is?Ground-water are derived from rain water and surface water, however passage through the ground and contact with soil for long periods, often many years, some time can alter the physical, chemical, and biological characteristics radically. For example, filtration through soil over long distance usually removes all suspended materials, including turbidity and bacteria. On the other hand, the slow movement increases opportunities for contacting and desolving chemicals present in the soils, and biological or physical-chemical reactions may either reduce or increase the concentrations of various constituents. The deference between ground and surface water is found in the solution of limestone deposits. Calcium carbonate(limestone) is only slightly soluble in at pH value of surface water. When rain water moved down through the top soil it may acquire substantial quantities of carbon dioxide produced in biological decomposition of organic matter. The solution of that carbon dioxide in water produces weak carbonic acid, which can react with calcium carbonate deposits to produce calcium bicarbonate, this mechanism increases the calcium content, and became much more likely to contain high concentrations of calcium then are surface water. Because of large storage volumes and long retention times, ground waters exhibit less variability in quality with time then do surface waters, even lakes. They tend to be much more uniform in temperature, chemical characteristics, and biological content. Filtration through soil usually removes essentially all of the suspended matter, including organism, but the mineral content of ground water usually is higher than that of surface water.
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