A boil-water advisory or boil-water order is a public health advisory or directive given by government or health authorities to consumers when a community's drinking water is, or could be, contaminated by pathogens.
Under a boil-water advisory (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 meters, boiling should be extended to 3 minutes, as the lower boiling point at high altitudes requires more time to kill such organisms.
BWAs are typically issued when monitoring of water being served to consumers detects Escherichia 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.
Some countries, like Canada, have publicly available maps showing the locations of boil-water advisories.
- National Research Council (U.S.). Committee to Review the New York City Watershed Management Strategy (2000). Watershed management for potable water supply: assessing the New York City strategy. National Academies Press. ISBN 978-0-309-06777-5. Retrieved 2011-04-11.
- A Guide to Drinking Water Treatment and Sanitation for Backcountry & Travel Use. Centers for Disease Control and Prevention. Accessed 2012-06-16.
- National Water Advisory Map The Water Chronicles. Accessed 2013-01-24.