Boiling water is the most fundamental and universally accessible method for making questionable water sources safe to consume. This simple process, which involves subjecting water to high heat, is highly effective at eliminating biological threats that cause waterborne illnesses. Understanding when this process is necessary and how to perform it correctly is the first step toward ensuring the safety of your drinking water supply.
Situations Requiring Water Boiling
Boiling water becomes necessary when the integrity of a water supply is compromised by potential biological contamination. The most common trigger is a public health directive known as a “Boil Water Advisory” or “Boil Water Notice.” These advisories are typically issued when monitoring detects microbial indicators of contamination or when a loss of water pressure suggests pathogens could have entered the distribution system.
Emergency situations also mandate boiling water, as infrastructure damage can easily disrupt water treatment and delivery. Events like floods, earthquakes, or power outages often lead to system failures, making the water unsafe until testing confirms otherwise. Boiling is also recommended when using water from an untreated source during outdoor activities like hiking or camping. Even clear streams can contain disease-causing microorganisms, making pretreatment essential.
How Boiling Purifies Water
The purification power of boiling water lies in the destructive effect of heat on biological contaminants. When water is heated, the high temperatures damage the structural components and disrupt the essential life processes of waterborne pathogens. Specifically, the heat denatures the proteins of microorganisms, which effectively kills or inactivates them.
A full, rolling boil is sufficient to eliminate virtually all common waterborne disease-causing agents, including bacteria, viruses, and protozoa. These pathogens are often resistant to standard chemical disinfectants like chlorine. While boiling is often referred to as “disinfection,” it is more accurately characterized as pasteurization, as it kills organisms capable of causing human illness without necessarily sterilizing the water completely.
Practical Steps for Effective Water Boiling
To effectively purify water, a few simple, sequential steps must be followed. If the water is visibly cloudy or contains heavy sediment, it should first be filtered through a clean cloth or coffee filter to remove the larger debris. This pre-treatment step reduces turbidity, allowing the heat to work more efficiently on the remaining microorganisms.
The water must then be brought to a full, rolling boil—one that continues vigorously despite stirring. For most locations, maintaining this rolling boil for at least one full minute is recommended. However, at elevations above 6,500 feet, water boils at a lower temperature due to reduced atmospheric pressure. To compensate, the boiling time must be extended to three minutes to ensure effective pathogen inactivation. After boiling, allow the water to cool naturally and store it in clean, tightly covered containers to prevent recontamination.
What Boiling Does Not Remove
While boiling is highly effective against biological threats, it is not a comprehensive water purification method. The process is largely ineffective at removing non-volatile chemical contaminants and heavy metals. Substances like lead, arsenic, nitrates, pesticides, and herbicides are stable at water’s boiling temperature and remain in the liquid.
Boiling can sometimes make the concentration of these substances worse. As the water evaporates during the process, the volume of water decreases, but the heat-resistant chemical contaminants stay behind. This results in the remaining water having a higher concentration of harmful pollutants than before boiling. For water known or suspected to contain chemical contamination, such as during a “Do Not Drink” advisory, boiling should be avoided, and bottled water must be used.