Boiling tap water is a widely recognized method for making water safer to drink, particularly in situations where the quality of the water supply is uncertain. This process involves heating water to its boiling point to inactivate or eliminate harmful substances. While boiling is an accessible and straightforward purification technique, it has specific applications and limitations that are important to understand for effective use.
What Boiling Effectively Removes
Boiling water effectively eliminates biological contaminants, a primary concern for waterborne illnesses. The high heat denatures proteins and damages microorganisms, rendering them inactive or destroying them. This process makes water safe from many disease-causing agents, similar to pasteurization. It reliably targets and inactivates pathogens like bacteria (E. coli, Salmonella, Campylobacter), viruses (Rotavirus, Hepatitis A), and parasites (Giardia, Cryptosporidium). These organisms cannot survive sustained exposure to boiling temperatures, typically 100°C (212°F) at sea level.
What Boiling Does Not Remove
Boiling does not remove chemical contaminants, heavy metals, or dissolved solids. Substances like lead, mercury, arsenic, and fluoride have significantly higher boiling points than water, meaning they remain in the water even after it boils. As water evaporates, the concentration of these heat-stable contaminants can increase, potentially making the remaining water more hazardous.
Chemical pollutants such as pesticides, herbicides, and industrial solvents are also unaffected by heat. Nitrates, often from agricultural runoff or sewage, are highly soluble and do not break down with heat, posing health risks, particularly for infants. Boiling water also does not remove microplastics or other dissolved solids, like minerals such as calcium and magnesium.
Best Practices for Boiling Water
To purify water effectively, bring it to a full, rolling boil with continuous, rapid bubbles. For most elevations, maintain this boil for at least one minute to inactivate harmful microorganisms. At altitudes above 6,500 feet (2,000 meters), extend the rolling boil time to three minutes.
After boiling, allow the water to cool naturally before consumption; do not add ice, as this can reintroduce contaminants. Store the purified water in clean, sanitized, food-grade containers with tight-fitting covers to prevent recontamination. Properly stored boiled water remains safe for drinking at room temperature for up to 24 hours, or up to three days if refrigerated. To improve the flat taste, pour it between two clean containers or add a small pinch of salt.
When Boiling is Not Enough
Boiling water is a valuable emergency purification method, but it is not a comprehensive solution for all water quality concerns. Its limitations mean it is insufficient when water contamination involves chemical pollutants or heavy metals. For example, boiling will not remove lead from old plumbing; it can even concentrate it. Agricultural runoff can also introduce pesticides and nitrates, and industrial spills might introduce various toxic chemicals, none of which are addressed by boiling.
When such contaminants are suspected, alternative treatment methods are necessary. Filtration systems designed to remove specific chemicals or heavy metals, or processes like distillation, may be required. Boiling should be considered a method for addressing biological threats, not a universal solution for all forms of water contamination.