You may have heard that boiling your water will make it safer to drink, However, it’s important to know the facts about boiling your water before switching on the stove. Boiling your water addresses only a small fraction of water quality concerns, and in some cases, it can make other issues worse.

Boiling water is great at killing waterborne pathogens (disease-causing agents). These include protozoa, bacteria, and viruses that attack cells or release toxins that harm the body. Many of these concerning pathogens can enter drinking water when it is contaminated with fecal matter. Sources of this contamination may include raw sewage overflow (especially during storms that flood urban areas), agricultural runoff, leaking sewer lines, and release from septic tanks. Fecal contamination is a major drinking water issue, so the government has protections in place to help prevent it–scroll down to learn more.

The disinfection process requires a one minute rolling boil, though some sources suggest a longer period of up to three minutes at high elevations and for larger water volumes. The heat from boiling water damages the structural components of pathogens, including their outer shells and important proteins, so they cannot survive.

There are some pathogens that can withstand extreme heat; however, evidence suggests that the most prevalent waterborne pathogens are rendered harmless by boiling water. These include:

Boiling water is not effective for removing most chemicals of concern, and may take water quality concerns from bad to worse. Boiling does not remove:

Some sources suggest that boiling water will effectively remove chlorine, but this process takes around 20 minutes and will not remove the chlorine that has combined with other substances.

Importantly, boiling off some of your water will concentrate the contaminants that boiling does not remove, meaning you will drink higher levels of these compounds per glass than you would prior to boiling. This can be very dangerous, and it is the primary reason that you should be careful in deciding whether to boil your water.

For example, a person whose water contains E. coli and low levels of nitrate may temporarily boil their water to kill the E. coli, but in doing so they will increase the nitrate concentration, perhaps to harmful levels.

Boiling water may also negatively impact the taste of water. It reduces dissolved gasses like oxygen and carbon dioxide, which leaves your water tasting flat and unappetizing.

Therefore, the Centers for Disease Control and Prevention (CDC) suggests that you aerate the boiled water by pouring it out of one container and into another, then allow it to sit for a couple hours. You can also add a pinch of salt to each liter of boiled water to overcome the flat taste.

You should boil your water only during a “boil water” order issued by the government, or during emergencies when you do not have access to disinfected water (ideally with an added filtration step, as described by the CDC). Whether you regularly boil your drinking water at home is ultimately up to you, but it may be time and energy-consuming, and unnecessary under normal circumstances. In the worst case, boiling your water may exacerbate other water quality issues you have, so it’s important to have detailed information about your water quality before making this decision.

Boiling your water is typically not a good solution for drinking water disinfection in the long term. There exist many treatment technologies that you can easily install in your home to prevent exposure to waterborne pathogens if contamination is an ongoing issue. Water filters (including micro-, ultra-, or nanofiltration and reverse osmosis), UV disinfection, and a chlorine drip system are some of the treatment systems that are effective in preventing waterborne pathogen contamination.

The answer to this question is different depending on your water source.

Public water systems have a number of strategies to protect their customers from microbial contamination. One widespread method for keeping public drinking water safe and free of contaminants is called the multiple barrier approach, which uses various tools and strategies to prevent contamination of drinking water from the source to the tap. This approach includes the protection of the source water, many treatment techniques in a row that provide redundancy, and proper management of the distribution system. Testing for every waterborne pathogen would be difficult and expensive, so water distribution systems are instead required to frequently test for water quality characteristics that indicate whether there are any issues with the treatment process, including turbidity.

In addition, these systems are required to test for total coliforms regularly and often (at a frequency proportional to the population served). Total coliforms is a group of bacteria that contains E. coli as well as a large number of related, non-harmful bacteria; they are used as an indicator of possible contamination, meaning that their presence may indicate contamination by harmful species but is not direct evidence of contamination. When a test comes back positive for total coliforms, the system must further test specifically for the infectious E. coli species. If a single test comes back positive for E. coli, or 5% of total coliform tests in the month are positive, the water system must report the violation to the state and the public. This may also result in a “boil water” notice.

Public water systems are also required to disinfect their water, which is typically accomplished by adding chlorine-based chemicals or by UV disinfection. And systems in contact with surface water are required to use chlorine and maintain a residual chlorine concentration to inactivate pathogens in the distribution system. It is important to note that some waterborne pathogens are resistant to chlorine disinfection. One example is Cryptosporidium, a protozoa most commonly introduced to water through animal waste. Only surface water systems serving over 10,000 people must monitor their source water for Cryptosporidium.

These regulations do not extend to private wells, which serve over 23 million households in the US, as estimated by the EPA. If you own a private well, you should test for coliform bacteria annually, and more frequently if you suspect contamination.