Annual Probability of Being Under a Boil Water Advisory

Boil water advisories affect approximately 15-20 million Americans each year (about 5% of the population). These advisories are issued when water systems may have been contaminated or when treatment systems fail, requiring residents to boil tap water before drinking, cooking, or brushing teeth.

The most common triggers for boil water advisories include water main breaks (the most frequent cause), loss of water pressure (which can allow contaminant infiltration), equipment or treatment failures, natural disasters (hurricanes, floods, earthquakes), and positive tests for bacteria (E. coli or total coliforms). Some advisories last only hours, while others (particularly after major disasters) can persist for weeks or months.

The largest recent boil water events include Jackson, Mississippi (2022, affecting 150,000+ residents for months), and various Texas communities during Winter Storm Uri (2021, affecting millions). Older water infrastructure is more prone to breaks and failures. The American Society of Civil Engineers gives US drinking water infrastructure a grade of C-minus, with an estimated $434 billion investment gap over the next 20 years. During a boil water advisory, water should be brought to a rolling boil for at least one minute (three minutes above 6,500 feet elevation).