E. Coli in Portland’s Water

Last week the City of Portland issued an emergency warning to all of its residents to “boil the water” because of the presence of E. Coli bacteria in the water.  While the notice was lifted 24 hours later, the announcement was enough to spook the local population and cause a run on bottled water.  Since then, a number of friends have ask me about the standards that are used to determine if water is safe.  Here’s a brief overview of how the water quality standards are set…

The Clean Water Act, passed by congress in 1972, requires states to identify the “beneficial uses” of water ways and sources and set “water quality standards” to protect those uses.  “Beneficial uses” include recreational use (swimming), use by industry, use for irrigation in agricultural, habitat for aquatic species, and human consumption (drinking). The state of Oregon has set standards unique to each beneficial use for various pollutants, and those standards must be approved by the EPA.

The water supplied to Portland (in this case, from the Mount Tabor reservoir) must meet the standards set out by the state of Oregon for the beneficial use of drinking. E. Coli, a bacterium associated with fecal matter, can produce toxins that are harmful to humans, and must be tested for at least 5 times a week in water supplies to major population areas. In the interest of protecting public health, the standards for bacteria are very conservative. When measuring for bacteria at such low levels, false positives are likely. Therefore, multiple positive tests within a given timeframe are required to determine if a water source is, in fact, in violation of the water quality standards for E. coli.

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