Can your water be too clean?

by (author unknown), Blue Gold, European Water Partnership Blog on Sep 20, 2007

from Water and Energy by Leslie


We’re all familiar with how vaccines work: you get a small dose of a nasty virus or other pathogen, your body works out how to fight it, and then you’re pretty much protected against coming down with the illness that the virus causes.


This semester, as part of the Water Resources Program at UNM, I am studying water reuse with Dr. Bruce Thomson. He assigned us an article by his colleague, Floyd J. Frost. Dr. Frost hypothesized that small amounts of some pathogens in drinking water can actually provide a protective immunity against disease.


He developed a study to test whether people who are exposed to small amounts of Cryptosporidium on a regular basis might be less susceptible to the gastrointestinal distress caused by a Cryptosporidium infection.


He studied people who got their drinking water from a good quality surface source. He tracked episodes of gastrointestinal illness among the sample populations and correlated those with levels of two antigens believed to be produced by the human body in response to Cryptosporidium. He found that those with at least moderately high levels of the antigens experienced significantly less outbreaks of gastrointestinal distress episodes.


More research is needed to fully understand what is happening. The study suggests that “a moderately strong serological response to a Cryptosporidium antigen group is related to a lower risk of enteric illness.” (pp 812-813) The implication is that ”f future improvements in water treatment reduce serological responses for users of surface water, then the risk of cryptosporidiosis will likely increase. Thus, reducing low-dose waterborne exposures may increase rather than reduce the risks of diarrheal and gastrointestinal illnesses.” (p813)


Obviously, this raises some difficult questions for those responsible for policy on water treatment standards. Can drinking water be too clean?

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