Quick Answer
Boiling tap water before drinking it is recommended to kill any disease-causing microbes that may be present. For most pathogens, heating water to a rolling boil for 1 minute is sufficient. At elevations above 6,500 feet, boil for 3 minutes. Boiling for longer may give an added margin of safety, but is not strictly necessary. Simply bringing water to a boil is adequate to make tap water safe to drink.
Why Boil Tap Water?
Boiling tap water before drinking is recommended as a simple way to remove or kill any pathogenic microorganisms (germs) that may be present in the water.
Tap water is not sterile and can contain harmful microbes such as bacteria, viruses, protozoa and parasites. Some common contaminants found in tap water include:
- Escherichia coli (E. coli) bacteria
- Salmonella bacteria
- Shigella bacteria
- Campylobacter bacteria
- Vibrio cholerae bacteria
- Yersinia enterocolitica bacteria
- Cryptosporidium parasite
- Giardia lamblia parasite
- Legionella pneumophila bacteria
- Norovirus
- Rotavirus
- Hepatitis A virus
While most tap water in developed countries is treated at water treatment plants to remove pathogens, contamination can still occur through leaks, groundwater seepage, or failures in treatment. Boiling water is an extra precaution to protect against consuming any pathogens that may get into the water.
How Does Boiling Water Remove Contaminants?
Boiling water is an effective method of water purification because heat kills microorganisms and pathogens by denaturing their proteins.
When water is heated to its boiling point of 212°F (100°C), the high temperature is sufficient to damage the cell structures of most disease-causing microbes, inactivating them so they are no longer infectious.
Specifically, boiling water:
- Kills bacteria – High temperatures break down the cell walls and structures of bacteria. Most bacteria cannot survive water that has been brought to a rolling boil.
- Kills viruses – The proteins and structures in viruses are also damaged by high heat. Viruses cannot reproduce or infect once boiled.
- Kills parasites – Parasites and their eggs (cysts) cannot withstand high water temperatures and die when boiled.
In addition to killing most pathogens, boiling also ensures the safety of water by removing heavy metals like lead and arsenic, as well as most chemical contaminants.
How Long Should You Boil Tap Water?
According to the Centers for Disease Control and Prevention (CDC), bringing water to a rolling boil for 1 minute is sufficient to make it safe to drink and for all cooking purposes.
The EPA recommends the following boil times for tap water:
- Rolling boil for 1 minute: Sea level to 6,500 feet elevation
- Rolling boil for 3 minutes: Over 6,500 feet elevation
Boiling water vigorously for 1 minute (sea level to 6,500 feet) or 3 minutes (over 6,500 feet) ensures that the water temperature has reached at least 212°F (100°C) throughout, which is hot enough to kill disease-causing germs.
Why 1 minute?
Heating water to 212°F and maintaining this temperature for 1 minute is sufficient to inactivate and kill pathogenic bacteria, viruses, and parasites. Studies have shown that E. coli, Salmonella, Vibrio cholerae and other harmful bacteria are eliminated within 30 seconds at a rolling boil. Giardia cysts are inactivated after 1 minute.
Why 3 minutes above 6,500 feet?
At higher altitudes above 6,500 feet, the boiling point of water decreases due to lower atmospheric pressure. So boiling for only 1 minute may not heat the water to high enough temperatures to kill pathogens. Boiling for 3 minutes allows the water to reach hot enough temperatures to sterilize it.
What about longer than 1 or 3 minutes?
Boiling water for longer time periods can provide an extra margin of safety by heating pathogens to higher temperatures. However, increasing the boil time much longer than 1 or 3 minutes is generally considered unnecessary.
For example, the Wilderness Medical Society recommends bringing water to a boil for 3-5 minutes when camping or hiking in remote areas. This extended 5 minute boil time ensures that pathogens like Giardia are neutralized if you happen to be at a higher altitude.
Does Boiled Water Need to Cool Before Drinking?
There is no need to cool down boiled water or wait for it to reach room temperature before drinking. It is safe to drink boiled water while it is still hot.
In fact, drinking boiled water hot has the advantage of killing any pathogens that may have been reintroduced during storage or handling after boiling. Very high temperatures keep water sterile, so drinking freshly boiled hot water provides maximal safety.
Is Hot Water as Effective as Boiled Water?
No, simply heating water to hot temperatures is not as reliable for making water safe to drink. Water needs to be brought to a rolling boil to effectively kill germs.
Heating water to temperatures below the boiling point can destroy some pathogens after prolonged exposure, but does not kill more resistant bacteria spores and some viruses.
Water should be boiled until large bubbles rise vigorously from the bottom of the pot to ensure the full volume has reached boiling temperature.
Tips for Boiling Tap Water
Here are some tips for safely boiling tap water:
- Bring water to a full rolling boil, not just bubbles around the edges.
- Boil tap water even if it is filtered.
- Boil for 1 minute (3 minutes over 6,500 feet elevation).
- Store boiled water in clean, covered containers.
- Refrigerate boiled water and use within 1-2 days.
- Do not boil water in the microwave – this does not heat evenly.
- Boil fresh water daily for babies under 6 months.
When is Boiling Water Recommended?
Boiling tap water before use is recommended in the following situations:
- Drinking Water – Boil water used for drinking, brushing teeth, making ice, mixing baby formula, cooking, etc.
- At-Risk Groups – Boil tap water for pregnant women, infants, young children, elderly, and those with weakened immune systems.
- After Disasters – Boil tap water after events like floods, earthquakes or power outages that may contaminate water.
- Traveling Abroad – Boil tap water when traveling in places with inadequate sanitation.
- Rural Water Systems – Those on private well water should periodically test and boil water.
Alternatives to Boiling
While boiling is the gold standard, other methods like filtration and chemical disinfection can also make water safer:
- Water filters remove many pathogens through mechanical trapping and adsorption.
- Disinfectants like chlorine, iodine and chlorine dioxide kill germs chemically.
- UV light systems inactivate microbes by damaging their DNA/RNA.
- Distillation involves evaporating then condensing water to purify.
However, boiling remains the simplest, most accessible and reliable method for households to treat water.
Safety of Tap Water
It is important to note that in developed countries, tap water is treated and monitored to meet safety standards. Outbreaks are rare, but contamination can occur.
The EPA regulates over 90 potential water contaminants and sets maximum allowable levels. Public drinking water systems are required to regularly test for pathogenic bacteria and viruses.
However, issues like lead contamination in aging pipes, pollution leakage or broken water mains can introduce pathogens. Boiling provides an extra barrier against consuming any dangerous organisms.
Is all tap water unsafe?
No, tap water supplied by public water systems in developed countries is generally safe. However, since there is always a small risk of contamination, boiling is recommended as a precaution.
Can boiling remove lead from water?
Yes, boiling can effectively remove lead from tap water by evaporating the water as steam. Lead contamination can occur from corroded lead pipes, lead solder and some brass plumbing fixtures.
Does boiling remove chlorine from tap water?
Yes, boiling water for 5-10 minutes can help remove chlorine added during water treatment. Many people boil water to reduce residual chlorine levels that can alter taste, odor and color.
Conclusion
Boiling water before drinking and cooking is recommended to provide a simple additional barrier against waterborne illnesses. Heating tap water to 212°F (100°C) and maintaining a rolling boil for 1 minute (3 minutes above 6,500 feet elevation) can effectively kill viruses, bacteria, parasites and other pathogens that may be present in the water.
While not a major concern in developed countries, taking this extra precaution ensures safety against any potential contamination that could occur in tap water systems. Boiling remains the easiest, most reliable method of water purification available.
