Centrally Treated Water Supplies

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As a company, we support the practice of large-scale, central treatment of drinking water by professionals. The municipal waterworks generally do an excellent job, and they make our job easier. But the smaller the customer base, the fewer resources are available, and the smallest systems have the most difficulty meeting the requirements. Also, the smaller the system, the more likely it has a ground water source, and those generally require less treatment than water from lakes and rivers. Surface water often contains “color” (tannins) and high turbidity which must be coagulated with special chemicals before filtering. These tannins are also the major source of unwanted byproducts of chlorine disinfection such as THMs and many other chlorinated organic compounds. Many surface waters are mostly snow-melt or rain water with relatively little total mineral content, called Total Dissolved Solids (TDS). This allows the water to be corrosive or aggressive to plumbing materials so that asbestos fibers and lead, zinc, cadmium, copper, and iron corrosion byproducts leach into the water from asbestos-cement pipe, brass fittings, lead-based solder, and copper and galvanized pipes. The microbiological quality of tap water is generally very good as the water leaves the waterworks – often less than 10 HPC (Heterotrophic Plate Count), but after a few hours or miles of transit through the distribution system, the chlorine dissipates and allows the bacteria that survived disinfection to multiply. In addition, biofilms containing many species build up and flake off into the water. It is important to remember that less than one-half of 1% of the potable tap water produced by large waterworks is actually consumed by people. The rest is used for flushing toilets, washing everything from laundry to streets, watering lawns, fighting fires, etc.