With so much water on the earth, you may wonder, why is the pollution of the current available supply such an issue? Because desalinating sea water is costly and distilled water is not the answer to healthy water as it lacks essential minerals.
The question: “Can I trust my tap water?” not surprisingly depends on where you live.
Allegedly about 90% of the earth’s surface water is infected to varying degrees with parasites such as cryptosporidium and giardia, bacteria such as E coli, Vibrio cholera and salmonella, and roto or polio viruses. Some groundwater also has nitrates from excessively fertilized soil. They are easily converted to nitrites which are carcinogenic.
The most worrying inorganic contaminants in water include excess aluminum, arsenic, cadmium, chromium, copper, cyanide, fluoride, iron, lead, manganese, mercury, sulfate, thallium and zinc. The USA’s Environmental Protection Agency is something of a gold standard for water quality and of its 54 listed organic pollutants the most harmful include alachlor, acrylamide, atrazine, benzene, benzopyrene, carbofuran, chlordane, carbon tetrachloride, chlorobenzene, dioxin, heptachlor, PCB’s (polychlorinated biphenols), toluene and vinyl chloride. Most of these stem from petroleum refineries, chemical factory discharge, leaching of landfills or pesticide residue. Any radio active substances are clearly not a boon. South Africa has a far less extensive list, known as the SANS 241 2005 Drinking Water Specifications, published on the DWA web site.
Even after treatment, some products remain in concentrations regarded as too high for human health. Scientific evidence also steadily recommends reducing prescribed limits, so that when the permitted level of arsenic of 50 micrograms/liter, was shown to pose a risk of cancer, the EPA revised the levels. All municipal water has chlorine added, regarded as harmless enough in liquid form in approved amounts, but harmful as a gas (hence in hot water showers) or in combination with other chemicals resulting in toxic chlorine byproducts. As effective as it is against most harmful waterborne diseases, chlorine has no impact on Cryptosporidium or Giardia, which bypass poorly managed filtration plants.