A Boil Water Notice (BWN) is a public health announcement issued by water utilities or regulatory bodies. This advisory instructs consumers to use boiled or bottled water for consumption due to the potential presence of harmful microorganisms in the tap water supply. The notice is a precautionary measure designed to prevent waterborne illness when drinking water safety cannot be guaranteed.
Why Notices Are Issued
Water authorities issue a Boil Water Notice when an event compromises the integrity of the water distribution system, creating a risk that contaminants could enter the supply. A common trigger is a sudden loss of water pressure, often below 20 pounds per square inch (psi). This pressure loss allows groundwater or other sources of contamination to seep into the pipes and frequently follows major infrastructure failures, such as a large water main break.
Notices are also issued due to power outages at water treatment plants or pumping stations, which disrupt the disinfection process or the movement of water. In some cases, a BWN follows routine water sampling that yields initial positive test results for indicator bacteria, such as total coliform or E. coli. Since definitive laboratory testing takes time, the notice is issued immediately as a precaution to protect public health while further investigation is underway.
Essential Steps for Boiling Water Safety
The primary action during a boil water notice is heating tap water to eliminate potential microbial threats. To effectively disinfect the water, bring it to a full, rolling boil for a minimum of one minute. This duration guarantees the water reaches a temperature sufficient to inactivate waterborne pathogens. If living at elevations above 6,500 feet, extend the boiling time to three minutes because water boils at a lower temperature at higher altitudes.
Once boiling is complete, allow the water to cool before use or storage. Transfer the cooled, treated water into clean, sanitized containers with tight-fitting covers to prevent recontamination. This boiled water must be used for all activities where water could be ingested, including drinking, preparing food, making ice, and mixing baby formula. Other activities requiring boiled water include washing produce eaten raw and brushing teeth.
Dishwashing and Hygiene
Dishwashers are safe if they have a sanitizing cycle or reach a final rinse temperature of at least 150°F. Hand-washed dishes should be rinsed in a sanitizing solution or allowed to air dry after a hot wash. For personal hygiene, bathing and showering are typically safe, provided no water is swallowed, but caution should be used when bathing infants and young children.
Health Risks Addressed by Boiling
Boiling is a highly effective method of water disinfection because the heat kills or inactivates waterborne pathogens. The high temperature denatures the proteins and damages the structural components of microorganisms, rendering them non-infectious. This thermal process is effective against common pathogenic bacteria, such as E. coli, Salmonella, and Shigella.
The heat also eliminates viruses, including norovirus and rotavirus, which frequently cause gastrointestinal illness. Boiling is also sufficient to kill protozoa, such as Giardia and Cryptosporidium, which are often resistant to chemical disinfectants. While boiling makes water microbiologically safe, it does not remove chemical contaminants like heavy metals, pesticides, or excess nitrates, which still require bottled water for safe consumption.
How a Boil Water Notice is Lifted
A Boil Water Notice is only officially canceled once the water system has been repaired and a series of water quality tests confirm the water’s safety. Authorities must first correct the underlying problem, such as fixing a broken main or restoring proper disinfection at the treatment facility. Once the system is stabilized, water samples are collected from various points within the affected distribution area.
The regulatory standard requires multiple sequential samples to be taken, often over a 24- to 48-hour period. To lift the notice, all samples must consistently test negative for indicator bacteria, confirming the absence of microbial contamination. The public is then notified that the advisory is lifted, typically through the same communication channels used for the original notice. After the notice is canceled, customers should flush all cold water faucets for several minutes to clear stagnant water and replace disposable filters in refrigerators and other appliances.