A boil water advisory (BWA) is issued when the water supply is suspected or confirmed to be contaminated with disease-causing microorganisms (bacteria, viruses, or parasites). The advisory instructs residents to boil tap water before consuming it, which kills these pathogens. When the BWA is officially lifted, the public water main system is delivering safe, treated water. However, water sitting stagnant within your home’s internal plumbing and appliances during the advisory remains unsafe. Immediate action is required to flush out the contaminated water and replace it with the clean supply.
Standard Procedure for Clearing Cold Water Lines
Restoring safe water involves flushing the cold water lines at every fixture in the home. This process draws fresh, treated water from the public main line into your private plumbing system. For most residential cold water taps, run the water for a minimum of three to five minutes to ensure the full volume of water in the internal pipes is completely exchanged.
Begin the flushing sequence with the fixture located furthest from where the water main enters the house, then work your way back toward the entry point. Fully open the cold water tap and let it run until the temperature becomes noticeably colder and consistent. This temperature change is a physical indicator that the main line water has arrived. For single-lever faucets, ensure the lever is pushed fully to the cold side to bypass the hot water tank.
Do not overlook utility water outlets, such as basement sinks or outdoor hose bibs, which need to be flushed for the same duration. Toilets must be flushed multiple times to clear the water held within the tank and the bowl. Similarly, run shower heads on the cold setting for at least three to five minutes to ensure the water sitting in the pipe is completely replaced.
Special Instructions for Appliances and Hot Water Systems
Appliances and systems that hold water internally require specific attention beyond simple line flushing. Point-of-use water filters (in refrigerators, faucets, and under-sink systems) are not designed to remove the microbial contaminants associated with a BWA. If water ran through these filters during the advisory, the filter media may be compromised and should be removed, discarded, and replaced with a new cartridge after the lines are flushed.
Hot water systems need a more prolonged flush because the tank holds a large volume of water. To clear the water heater and associated pipes, run all hot water faucets until the water runs cool, indicating the stored tank water has been replaced. This may take around 15 minutes for a typical 40-gallon tank, or up to 30 minutes for an 80-gallon tank or larger. If the water heater temperature was set below 120°F, consult a professional, as a full draining and disinfection of the tank may be necessary.
Automatic ice makers must be completely emptied of existing ice, as the cubes were made with contaminated water. After flushing the refrigerator’s water dispenser, discard the first three batches of new ice produced to ensure the entire water line is clean. Devices like humidifiers, CPAP machines, and nebulizers that use stored water must have their reservoirs emptied, rinsed with clean water, and sanitized according to the manufacturer’s instructions. Water softeners should be run through a full regeneration cycle to flush out any held water.
Cleaning and Disposing of Contaminated Items
Any water collected or stored during the advisory, including mixtures like prepared baby formula or water given to pets, must be safely discarded. This ensures no one accidentally consumes the unsafe water. Discard all ice made during the advisory, as freezing does not kill the microorganisms.
Sanitizing food preparation surfaces and containers is the final step to eliminate cross-contamination. Household dishwashers are safe to use for sanitizing dishes if they have a hot water setting that reaches at least 150°F or a dedicated “sanitize” cycle. For surfaces, utensils, and containers that cannot be run through a dishwasher, prepare a mild bleach solution for manual sanitization. An effective ratio for a food-contact surface sanitizer is one teaspoon of unscented liquid household bleach mixed with one gallon of warm water. Allow the items to remain in contact with this solution for at least one minute, then let them air dry.