Here’s Why You Should Never Reboil Your Water

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

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 that water be re-boiled?


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

Here’s Why You Should Never Reboil Your Water

In fact, 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 shown to be harmful to both humans and animals. Strangely, nitrosamines are allowed to be added to certain foodstuffs without any 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 heart and blood vessels, and causes skin damage.

Arsenic is an abundant element found in the earth’s crust. As such, it is highly concentrated in rocks and soil – this can lead to the chemical being leaked 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 the chemical concentration of arsenic and increases 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 at reducing 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. It is also strongly recommended to have water wells tested at least once of year to prevent and mitigate and problems.


As the case with arsenic, fluoride cannot be removed from water through boiling. As also the case with arsenic, reboiling water increases the chemicals’ concentration levels and increases the likelihood of adverse health effects.

To date, many local governments continue to add measured doses of fluoride to water supplies. This is done in 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.

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