Have you ever wondered if it’s okay to reboil water and drink it like many of us do with our tea kettles?
Reboiling water refers to the practice of boiling it, allow it to cool below the boiling point, and then boiling it again. Have you ever wondered what happens to water chemistry when you reboil water? Is it still safe to drink?
If you have perfectly pure distilled deionized water, nothing will happen if you reboil it. However, most of us use ordinary tap or well water, which contains dissolved gases and minerals. The chemistry of the water changes when you boil it because boiling drives off the volatile compounds and dissolved gases. There are many cases in which this is desirable. However, if you boil the water too long or reboil it, you risk concentrating certain undesirable chemicals that may be in your water. Examples of chemicals that become more concentrated include nitrates, arsenic, and fluoride.
There is a concern that reboiled water may lead a person to develop cancer. This risk is not unfounded, but it is small. While the boiled water is fine, increasing the concentration of toxic substances may put you at risk for certain illnesses, including cancer. For example, excessive intake of nitrates has been linked to methemoglobinemia (elevated level of a certain type of hemoglobin in red blood cells, which can cause tissue hypoxia, or shortage of oxygen, which can lead to serious health conditions) and certain types of cancer. Arsenic exposure may produce symptoms of arsenic toxicity, and has been associated with some forms of cancer. Even “healthy” minerals may become concentrated to dangerous levels. For example, excessive intake of calcium salt, commonly found in drinking water and mineral water, can lead to kidney stones, hardening of the arteries, arthritis, and gallstones.
The bottom line is that generally boiling water, allowing it to cool and then reboiling it does not present much of a health risk. So, if you keep water in a tea kettle, add water when the level gets low, and you aren’t likely to endanger your health. It’s best if you don’t let water boil completely down, which concentrates minerals and contaminants (not to mention possibly ruining your tea kettle). If you reboil water, it’s better to do it once or at most twice, rather than make it your standard practice. Pregnant women and persons at risk for certain illnesses may wish to avoid reboiling water rather than risk concentrating hazardous chemicals in the water.
Jeffrey Bellomo, Esq.
Excerpts of this blog were taken from an article by Anne Marie Helmenstine, Ph.D.