Boiling water is both a common practice and one that is beneficial to our health. When water is boiled, some harmful substances are effectively removed. However, if for some reason the water cools, should you reboil it?

The answer is no, since reboiling the water allows certain gases and chemical compounds to concentrate. These chemical reactions and the the proliferation of certain gasses can harm our health.

Here’s Why You Should Never Reboil Your Water

If you boil the water too long or reboil it, you risk concentrating certain undesirable chemicals that may be in your water. ­– Dr. Anne Marie Helmenstine, Ph.D., Chemist

There is concern amongst health professionals that reboiled water can cause certain types of cancer. Chemicals that become more concentrated include nitrates, arsenic, and fluoride – these substances are toxic. Further, mineral concentration can also be harmful – concentrations of calcium salt, for example, can lead to the development of kidney stones.

The most significant risks are due to the accumulation of three toxic chemicals mentioned earlier – nitrates, arsenic and fluoride. Let’s delve into what makes these chemicals hazardous to our health.



Excessive intake of nitrates has been lined to conditions such as methemoglobinemia – an abnormal blood disorder – along with certain types of cancer. Another common way that nitrates are ingested is in the form of sodium nitrate – a preservative that is found in some processed meats, such as lunch meats, bacon and jerky. This nitrate is thought to increase the risk of heart disease and other types of illness. Sodium nitrate can potentially damage blood vessels – hardening and narrowing the arteries, leading to an increased risk of cardiovascular disorders.

When water is reboiled, nitrates in the water are reheated. This exposure to heat effectively converts nitrates into nitrosamines – a carcinogenic. Nitrosamines are harmful to both humans and animals. Strangely, nitrosamines can be added to certain foodstuffs without restriction. Reboiled water contains nitrosamines, as do certain processed foods, beers and some cheese products.

The dangers of nitrosamines and other variations of nitrates are numerous. Certain studies have demonstrated an increased risk in Alzheimer’s, Parkinson’s and Type 2 diabetes. Other diseases linked to nitrates are leukemia and lymphoma, along with cancer of the bladder, colon, esophagus, ovaries and pancreas.


A 1999 study released by the National Academy of Sciences demonstrates that arsenic in drinking water causes bladder, lung, and skin cancer. Arsenic can also potentially cause kidney and liver cancer. This same study shows that arsenic harms the central and peripheral nervous systems, damages the heart and blood vessels, and causes skin damage.

Arsenic is an abundant element from the earth’s crust. As such, occurs naturally and abundantly in rocks and soil, which can leak the chemical into water supplies.  Industrial activities can also produce high levels of arsenic, increasing the risk of water contamination.

Boiling water does not remove arsenic. However, reboiling water increases arsenic’s chemical concentration and health risk. According to the Center for Disease Control and Prevention (CDC), certain water treatment methods – reverse osmosis, ultra-filtration, distillation, or ion exchange – may be effective to reduce the levels of arsenic.

The CDC recommends contacting a local health department for methods of reducing arsenic levels in drinking water. If drinking from a private well, a state certification officer can provide a list of laboratories that will perform tests on drinking water.  CDC also recommends for you to test water wells at least once of year to prevent and mitigate any problems.



As is the case with arsenic, boiling does not remove fluoride. As with arsenic, reboiling water increases the chemicals’ concentration levels and increases the likelihood of adverse health effects.

To date, many local governments continue adding measured fluoride doses to water supplies. This is an attempt to reduce the risk of dental decay. However, mounting evidence has resulted in cities and towns reevaluating this common practice.

One commonly cited study on the harmful effects of fluoride was conducted at Harvard University, where researchers determined a correlation between increased levels of fluoride and cognitive impairment. The study, funded by the National Institutes of Health, concluded that children living in areas of highly fluoridated water had lower IQ’s than children who did not.

The study’s researchers wrote this troublesome summarization of their findings:

In conclusion, our results support the possibility of adverse effects of fluoride exposures on children’s neurodevelopment.