Boil-water advisory

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A boil-water advisory (BWA), boil-water notice, boil-water warning, boil-water order, 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.^[1]

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,^[2] 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. ^[1]

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).^[3]