Boiling tap water is a time-tested and highly effective method for disinfection, serving as the most immediate way to eliminate disease-causing microorganisms. This process of thermal inactivation works by exposing pathogens like bacteria, viruses, and protozoa to high heat, damaging their structural components and denaturing the proteins essential for their survival. When done correctly, boiling water provides a reliable barrier against waterborne illnesses. The Centers for Disease Control and Prevention (CDC) and other public health organizations consider it a foundational technique for water safety.
When Is Boiling Necessary?
The general public should boil tap water in specific situations where the safety of the municipal supply is compromised or unknown. The most common trigger is a formal “Boil Water Advisory” issued by local authorities, typically following a major incident like a water main break, a loss of pressure in the distribution system, or a failure at a water treatment plant. Other circumstances demanding water boiling include natural disasters such as floods or power outages that disrupt the normal water treatment and pumping processes. In an emergency, or when using water from an untreated source like a stream during camping or travel, boiling becomes a necessary precaution. It is a temporary measure designed to provide a safe supply until the underlying issue is resolved.
The Standard Procedure for Disinfection
The time required to boil water for safety depends on the elevation. For locations at or below 6,500 feet (2,000 meters), the standard procedure is highly effective against common waterborne pathogens. The water must first be brought to a full, vigorous “rolling boil,” characterized by large, continuous bubbles that do not stop when the water is stirred. Once a rolling boil is achieved, the water must continue to boil for one full minute to ensure complete thermal inactivation of microorganisms. This duration is sufficient to kill major waterborne bacterial and protozoan pathogens, including Giardia and Cryptosporidium. If the water is visibly cloudy, filter it through a clean cloth or coffee filter before boiling; afterward, remove the heat source and allow the water to cool before being used.
Adjusting Boiling Time for High Altitudes
A longer boiling time is required when disinfecting water at higher elevations due to the relationship between altitude and atmospheric pressure. As elevation increases, the atmospheric pressure decreases, causing water to boil at a lower temperature. For instance, at 6,500 feet, water boils at roughly 200°F (93°C), which is below the sea-level boiling point. Because the disinfection process relies on both temperature and time, the lower boiling temperature necessitates an extended exposure period to achieve the same level of safety assurance. For any location above 6,500 feet (2,000 meters), the water must be boiled for a minimum duration of three full minutes.
Post-Boiling Steps and Safe Storage
Once the water has been boiled, it must be handled correctly to prevent recontamination and improve its quality. Allow the water to cool completely without removing the lid from the container, which shields it from airborne contaminants. Boiling often causes a flat taste due to the loss of dissolved gases, which can be remedied through aeration. Aeration involves pouring the cooled water back and forth several times between two clean, sanitized containers to reintroduce oxygen. It is important to remember that while boiling eliminates pathogens, it does not remove chemical contaminants such as heavy metals or nitrates, and can even concentrate non-evaporating substances like lead.
The safe storage of disinfected water requires using clean, food-grade containers that have been sanitized before filling. The containers should be airtight and stored in a cool, dark place away from direct sunlight. Properly stored boiled water can remain safe for an extended period, though replacing it every six months is recommended for the best quality and taste.