Boil-water advisory
water safety directive
A boil-water advisory (BWA), boil-water notice, boil-water warning, boil-water order, boil ban, or boil order is a public-health advisory or directive issued by governmental or other health authorities to consumers when a community's drinking water is or could be contaminated by pathogens.
Under a BWA, the Centers for Disease Control and Prevention recommends that water be brought to a rolling boil for one minute before it is consumed in order to kill protozoa, bacteria, and viruses. At altitudes above 2,000 metres (6,600 ft), boiling should be extended to 3 minutes, as the lower boiling point at high altitudes requires more time to kill such organisms. A boil water advisory usually lasts up to 24-48 hours, but sometimes more.
BWA's are typically issued when monitoring of water being served to consumers detects E. coli or other microbiological indicators of sewage contamination. Another reason for a BWA is a failure of distribution system integrity evidenced by a loss of system pressure. While loss of pressure does not necessarily mean the water has been contaminated, it does mean that pathogens may be able to enter the piped-water system and thus be carried to consumers. In the United States, this has been defined as a drop below 20 pounds per square inch (140 kPa).
History
John Snow's 1849 recommendation that water be "filtered and boiled before it is used" is one of the first practical applications of the germ theory of disease in the area of public health and is the antecedent to the modern boil water advisory. Snow demonstrated a clear understanding of germ theory in his writings.
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