A boil water warning is a public health directive issued by water utilities or local agencies to alert consumers that their drinking water may be contaminated with disease-causing microorganisms. This advisory signals the presence of pathogens such as bacteria, viruses, or parasites that can cause gastrointestinal illness. The purpose of the warning is to prevent waterborne disease outbreaks by instructing the public to make their tap water safe before use. It is a precautionary measure until the water quality can be confirmed as safe for consumption.
Why Authorities Issue Boil Water Warnings
A boil water warning is typically triggered by an event that compromises the integrity of the water distribution system or the effectiveness of the treatment process. One common cause is a loss of water pressure, often falling below 20 pounds per square inch, which allows contaminants from the ground to seep into the pipes. Infrastructure failures, such as water main breaks or damage from construction, can also introduce harmful substances into the clean water supply. Natural disasters like floods or severe storms may overwhelm a treatment facility, introducing high levels of turbidity or raw sewage. Authorities may also issue a warning based on initial testing that confirms the presence of microbiological indicators, like E. coli, which signals sewage contamination. In many cases, the advisory is issued as a precaution immediately following an event while comprehensive testing is underway.
Essential Steps for Safe Water Use
The most reliable method for purifying water during an advisory is to heat it to a full, rolling boil. This high temperature effectively destroys pathogenic protozoa, bacteria, and viruses. The water should be allowed to boil vigorously for a minimum of one minute before removing it from the heat source. After boiling, the water must be allowed to cool before it is used or transferred to a clean, covered container for storage.
For residents at high elevations, specifically above 6,500 feet, the boiling time must be extended to three minutes. This extension compensates for the lower boiling point of water at reduced atmospheric pressure, ensuring sufficient thermal exposure to inactivate microorganisms.
If boiling is not possible, chemical disinfection is an emergency alternative using unscented household bleach containing 5% to 9% sodium hypochlorite. If the tap water is clear, add eight drops of bleach to one gallon of water, mixing thoroughly and allowing it to stand for at least 30 minutes. For cloudy or discolored water, first strain it through a clean cloth to remove sediment, then double the bleach concentration to 16 drops per gallon.
Guidelines for Specific Household Activities
Any water intended for drinking, making ice, or preparing food must be purified either by boiling or by using commercially bottled water. This includes water used for brushing teeth. Ice made during the advisory must be discarded as freezing does not kill pathogens.
When washing dishes by hand, first wash and rinse them with hot water. A sanitizing rinse should then be prepared by adding one teaspoon of unscented household bleach to one gallon of warm water, and the rinsed dishes should soak in this solution for at least one minute. Dishwashers are acceptable to use only if they have a sanitizing cycle or can reach a final rinse temperature of at least 150°F (66°C).
For preparing infant formula, use bottled water or water that has been brought to a full boil and cooled. Bathing and showering are generally considered safe, but care must be taken not to swallow the water. Infants or small children should be closely supervised. Pets should also be given boiled and cooled water, as they are susceptible to the same waterborne diseases as humans.
How a Warning is Lifted
To lift a boil water warning, the water utility must demonstrate that the system is free from contamination by collecting multiple water samples over a specified time period. These samples are sent to a certified laboratory to confirm the absence of harmful bacteria, a process that often requires a series of negative test results, typically spanning 24 to 48 hours. The advisory is officially rescinded only after the source of the contamination has been resolved and the water quality meets safety standards.
Once the warning is officially lifted, consumers must flush their household plumbing. Run all cold water faucets for a minimum of five minutes to clear out any potentially lingering contaminated water from the pipes. Empty any ice from automatic ice makers made during the advisory, and run the ice maker two to three times before the ice is consumed.