OVERVIEW

The principal health risk from drinking water in most locations is waterborne diseases from microbial contamination. According to the World Health Organization, an estimated 1.7 million deaths a year can be attributed to unsafe water supplies. Within the United States, waterborne diseases are a lower risk, but serious outbreaks still occur with some regularity. The Centers for Disease Control and Prevention (CDC) reported that for the 24-month period 1999 2000, there were 39 outbreaks of waterborne disease associated with drinking water in 25 states. Of the outbreaks for which the cause was identified, 90% were associated with pathogens, and the remainder were associated with chemical poisoning. Most outbreaks in community systems are a result of improper treatment or breaks in the distribution system that allowed for system contamination. Consequently, recent regulations have emphasized improved microbial controls through multibarrier techniques including improved watershed protection to minimize contamination at the source, filtration for contaminant reduction, disinfection for inactivation of the remaining pathogens, and residual disinfectant for the distribution system. Also, recognizing that encysted waterborne protozoans are more resistant to traditional disinfection practices, the regulations are forcing higher levels of disinfection and use of alternative technologies. Concurrently, other regulations seek to reduce the levels of disinfectant chemicals and their reaction byproducts, which are considered long-term health risks. This, then, is the designer s challenge, to provide comprehensive microbial reduction to minimize the risk of waterborne disease while also minimizing the formation of disinfection by-products.

This chapter provides...