Boiling sink water is a reliable and accessible method for eliminating biological threats, particularly during a water advisory or emergency. This heat-based process effectively deactivates disease-causing microorganisms that may be present in a water source. However, boiling is not a complete purification system, as it only addresses living organisms and leaves behind a significant range of chemical contaminants. Understanding this distinction is important for making informed choices about the safety of your drinking water.
How Boiling Purifies Water
Boiling purifies water through a process known as thermal disinfection or pasteurization, which targets and destroys waterborne pathogens. When water reaches its boiling point, typically 100°C (212°F), the intense heat damages the structural components of microorganisms. This thermal energy causes the proteins within the cells of bacteria, viruses, and protozoa to denature, rendering them inactive and unable to cause illness.
This method is highly effective against common waterborne culprits like Escherichia coli (E. coli), norovirus, and the parasites Giardia lamblia and Cryptosporidium. The destruction of these pathogens happens quickly once the water is brought to a rolling boil. Studies have shown that many waterborne pathogens are inactivated at temperatures significantly below the boiling point, sometimes as low as 65°C (149°F) with sufficient exposure time.
Maintaining a rolling boil for a specific duration ensures the heat penetrates all parts of the water and fully deactivates resilient organisms, such as protozoan cysts. While this process is extremely effective against biological contamination, it is not considered sterilization, which would eliminate all organisms, including harmless spores.
Contaminants Boiling Cannot Remove
Boiling separates water molecules from biological life, but it fails to remove non-biological contaminants, which are a concern in municipal and well water. Chemical contaminants, including heavy metals like lead, arsenic, and mercury, are unaffected by boiling. These substances have boiling points far exceeding that of water and will remain dissolved in the liquid.
Persistent chemical threats, such as nitrates from agricultural runoff, pesticides, and “forever chemicals” (PFAS), also do not break down or evaporate through boiling. Furthermore, total dissolved solids (TDS), which include minerals and salts, are left behind. If the initial concentration of these non-volatile substances is high, boiling the water can actually make the situation worse.
As water turns to steam during the boiling process, the volume of water decreases, but the mass of dissolved chemical contaminants does not. This evaporation concentrates the remaining chemicals, increasing their level in the final volume of drinking water. Therefore, relying on boiling alone when chemical contamination is suspected can inadvertently lead to a higher intake of toxic substances.
Step-by-Step Guide for Safe Boiling
The first step in safely boiling water is to address visible cloudiness or debris, such as suspended particles like mud or sediment. If the water is cloudy, it should first be filtered through a clean cloth, paper towel, or coffee filter to remove the larger particulates. Alternatively, the water can be left to settle for several hours, and the clearer water from the top can be carefully poured off for boiling.
Next, the clear water should be brought to a full, rolling boil over a heat source. A rolling boil is vigorous, continuous bubbling that ensures the water has reached the required temperature for disinfection. The water must be held at this rolling boil for at least one full minute to guarantee pathogen elimination.
For locations above 6,500 feet (about 2,000 meters), the boiling time must be extended to three minutes. This extended duration compensates for the lower atmospheric pressure, which causes water to boil at a slightly cooler temperature. After boiling, the water should cool naturally before consumption.
Once cooled, the disinfected water should be stored in clean, covered containers to prevent recontamination. If the boiled water has a flat taste, which is common due to the removal of dissolved gases, the flavor can be improved by pouring the water back and forth between two clean containers to aerate it. Adding a small pinch of salt per quart of water can also help improve the taste.
When to Choose Alternative Purification Methods
Boiling is insufficient when the contamination risk is primarily chemical, such as from industrial runoff, agricultural areas, or old pipes. In these scenarios, the danger is not from living organisms but from heat-stable toxins that boiling will concentrate. If you are under a “Do Not Drink” advisory that specifies chemical contamination, boiling should not be used.
Chemical Contamination Solutions
Alternative methods address heat-resistant contaminants. Activated carbon filtration can effectively remove chlorine, improve taste, and reduce certain chemicals and volatile organic compounds. Reverse osmosis systems are necessary to remove heavy metals, nitrates, and high levels of total dissolved solids.
Biological Contamination Alternatives
In situations where heat or fuel for boiling is unavailable, such as during backpacking or a prolonged power outage, chemical disinfection is an alternative. Water purification tablets containing iodine or chlorine can kill most biological pathogens, though they are less effective against robust parasites like Cryptosporidium. Ultraviolet (UV) light purifiers inactivate pathogens by damaging their DNA, but the water must be perfectly clear for the UV light to work effectively.