Boiling tap water is a time-tested method of disinfection, reliably used to render water safe for consumption. This practice eliminates waterborne illness by relying on sustained high heat to neutralize biological threats. While modern public water systems deliver safe drinking water under normal conditions, boiling remains the most accessible and effective emergency response to potential microbial contamination.
When Boiling Tap Water is Necessary
Boiling water is typically unnecessary for residents served by public water systems operating under routine conditions. These systems maintain stringent disinfection processes to ensure a continuous supply of safe drinking water. The necessity for boiling arises primarily during a “Boil Water Advisory,” a public health notification issued when water quality is compromised or at risk.
Advisories are commonly issued following events that disrupt the water distribution infrastructure, creating pathways for pathogens to enter the system. Examples include significant water main breaks, which cause a loss of system pressure, or natural disasters like floods that can overwhelm treatment facilities. An advisory is mandatory if routine testing detects the presence of indicator organisms, such as E. coli, suggesting potential sewage contamination. Private well owners must also consider boiling their water after any flooding event or if routine annual tests indicate bacterial presence.
What Contaminants Boiling Effectively Destroys
The effectiveness of boiling is directly linked to its ability to destroy biological pathogens. The heat from boiling water is powerful enough to kill or inactivate nearly all waterborne bacteria, viruses, and protozoa. These include disease-causing organisms such as Giardia, Cryptosporidium, Salmonella, and Norovirus.
The high temperature denatures the proteins within these microorganisms, rendering them harmless. This structural damage prevents them from reproducing or causing illness, making the water microbiologically safe.
Limitations of Boiling: What Heat Does Not Remove
A distinction must be made between microbial safety and chemical safety, as boiling water does not remove chemical contaminants. Substances that do not vaporize easily, such as heavy metals, nitrates, and other inorganic compounds, remain in the water even after boiling. These contaminants include lead, arsenic, mercury, and chromium.
The problem is compounded because boiling causes water to evaporate, which reduces the total volume of liquid. Since the non-volatile chemical contaminants stay behind, their concentration in the remaining water actually increases. For example, if tap water is contaminated with lead, boiling it will result in a higher, potentially more dangerous, concentration of lead per glass. Therefore, if chemical contamination is suspected, boiling is ineffective and can be counterproductive to safety.
The Proper Procedure for Boiling and Storage
The procedure must be followed precisely to ensure disinfection. First, if the water appears cloudy or turbid, it should be strained through a clean cloth or coffee filter to remove sediment before heating. This step ensures the heat can effectively reach all microorganisms.
The water must be brought to a full, rolling boil where large bubbles are vigorously rising from the bottom of the container. At sea level, this rolling boil must be maintained for at least one full minute. For elevations above 6,500 feet, the boiling time should be extended to three minutes due to the lower boiling point of water at higher altitudes. After boiling, the water should be allowed to cool naturally before consumption.
For storage, the cooled, boiled water should be transferred into clean, sanitized, and airtight containers to prevent re-contamination. If the boiled water has a flat taste due to the removal of dissolved oxygen, improvement can be achieved by pouring the water back and forth between two clean containers several times, a process known as aeration. Storing the water in a cool, dark location with tightly secured lids will maintain its safety.