Drinking Water and Disease: How Big is the Problem?

Estimates of the true magnitude of water-associated disease in this country are quite crude. It has been estimated that up to 900,000 people fall ill and up to 900 die annually from waterborne infectious diseases, but the basis of this estimate is not clear. Estimates range as high as 40 to 50 million cases of disease per year. What is clear is that officially recorded cases of waterborne disease represent only the tip of the iceberg. The significant barriers to conducting effective surveillance for waterborne microbial disease make accurate assessment nearly impossible. Assessing the health burden from waterborne chemicals is similarly daunting, because of the multiple routes of exposure that affect most people, the mobility of the population, and the long latency period between exposure and health effects, among other reasons.

Compounding the problem of inadequate surveillance is a regulatory system that can be slow to respond to advances in knowledge. Only a fraction of chemical water contaminants are regulated, and in some cases, such as arsenic, the current standards are acknowledged to be insufficient in protecting public health. Other chemicals, such as radon and a variety of pesticides, are known to pose health threats, but they are not regulated in drinking water. New requirements for detailed cost-benefit analysis may further erode the US. Environmental Protection Agency's (U.S. EPA's) ability to set standards that guarantee a conservative margin of safety.

For the latest available reporting period (1997-1998), 13 states reported 17 outbreaks associated with drinking water, and 18 states reported 32 outbreaks from recreational water. In total, more than 4,000 people fell ill from these outbreaks. While drinking-water outbreaks associated with surface water decreased by 20 percent since the previous reporting period (1995-1996), the proportion of outbreaks associated with groundwater sources increased by almost 30 percent.

The largest outbreak during the 1997-1998 period was caused by Cryptosporidium parvum, affecting 1,400 peopled drinking water from municipal wells that became contaminated by a spill of raw sewage. No deficiencies in water treatment were found. In fact, chlorine disinfection was in use, but apparently did not inactivate all of the Cryptosporidium introduced by the sewage contamination. Other etiologic agents associated with drinking-water outbreaks have included E. coli O157:H7, Giardia lamblia, and Shigella sonnei. Two of the 17 drinking-water outbreaks involved copper poisoning.

Almost three-fourths of the reported outbreaks were attributed to consumption of contaminated well water. Approximately 40 percent of the outbreaks were traced to inadequately treated water, and another 30 percent to contamination of distribution systems. (Adapted with permission from Drinking Water and Disease Primer: What Health Care Providers Should Know, Physicians for Social Responsibility, 2000.)