The Weak Link in the Provision of Safe Drinking Water

Abstract

The provision of safe drinking requires high quality water sources, treatment of the water, and its distribution. However, the first distribution systems in cities were designed for fire protection. In time they were extended to commercial and then to residential properties but their design then was the responsibility of the National Board of Fire Underwriters. Today, it is the Insurance Services Office, Inc., whose regulations are the text of AWWA's Manual M31, Distribution System Requirements for Fire Protection. Not one word relates to drinking water quality. Its only purpose is to assure adequate pressure and flows for fire protection. Apparently, drinking water quality is of no importance. Recent AWWA Water Quality Technology Conferences have had hundreds of papers on the degradation of water quality in distribution systems. Last year, AWWA compiled a 1,083-page volume, Water Quality in the Distribution System. The problems arise from defects in distribution systems designed for fire protection. Pipes and storage tanks need to be larger than necessary for drinking water systems, resulting in residence times that range to months. Long residence makes many water quality problems. Difficulties in maintaining disinfection, demanding higher doses of disinfectant, in turn result in excessive levels of disinfection by-products (DBPs), which are the most serious water quality health problems extant today. Another problem created by long residence times is the growth of biofilm on the insides of the pipes. The biofilms react with the disinfectants ,reducing their and creating growths that harbor the pathogens This leads to tuberculation that in time reduces the hydraulic capacity of the pipes. Still another problem created by the minimum 6- and 8-inch diameter pipes, which make up the larger lengths of pipes in the systems, are heavy pipes laid on soil with some 350 joints per mile, many of which, in time, leak. Loss of water may not be serious, but the frequent negative transient pressures that occur in the pipes have been found to suck contaminated groundwater into the pipe. One solution is a distribution system that carries only drinking water. It would not have hydrants and in most of the city, the pipes would be less than one inch, and laid with few joints. It would be a drinking water distribution system with none of the problems we face today. What about fire protection? In the last half-century, dual water systems have spread over the country. They were created to conserve drinking water by using reclaimed wastewater for the many nonpotable demands, including water for fire protection. More than 2,000 cities and towns have dual systems and more are being created every day. Most conventional water treatment plants are far short of being adequate despite statements that they meet EPA regulations. If only drinking water needs to be treated, the far lower cost would permit the adoption of membrane treatment, assuring drinking water of high quality Without question, new communities adopting such dual systems would deliver much higher quality water at lower cost. For existing communities, distribution systems would need to be introduced gradually when retrofitting for growth and as funds are available.