You’ve probably heard that it’s bad to boil water twice, or that the tea won’t be good. Have you ever wondered whether it’s safe to reboil water? Do you even know what reboiling water means?
Reboiling water it when you boil water, let it cool below its boiling point, and then boil it again. For example, you reboil water if you boil it in the microwave, forget about it, and then boil it again before taking it out. To some extent, you also reboil water when you top off the tea kettle, although that water is a mixture of fresh water and boiled water.
There’s a rather persistent idea that reboiling water while making a cup of tea is potentially harmful to your health, with some going so far as stating that regularly doing this even drastically increases your chances of getting cancer.
So Much Confusion!
If you search on the internet, this will be a really hard problem to figure out actually. There are so many contradicting articles about reboiling water. One source will say that it is toxic, while the next one will ensure we have nothing to worry about! So here are both sides to the story. Why do some people think it’s toxic to twice boil water, and others don’t?
All we want to know is what is safe to do… can you reboil already boiled water? Let’s find out!
What Happens When You Reboil Water
The claim is that when you reboil water, it changes the chemicals to become toxic.
If you have perfectly pure, distilled and deionized water, nothing will happen if you reboil it. However, ordinary water contains dissolved gases and minerals. The chemistry of the water changes when you boil it because this 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. The chemicals people are primarily worried about are nitrates, arsenic and fluorides.
Does Reboiled Water Cause Cancer?
There is a concern that reboiled water may lead a person to develop cancer. This concern is not unfounded. So basically, no. Drinking reboiled drinking water does not cause cancer.
But, it can increase your risk for cancer (from pesticides and other chemicals), methemoglobinemia (from nitrates in fertilizers), and arsenic toxicity (from arsenic, either natural or from waste). Lead and fluoride are also concentrated by reboiling. Lead comes from solder used in metal pipes, while fluoride either occurs naturally or is added to some public water supplies.
The Reality: It’s All About the Quality of Your Water
The reality is that the chemicals do become more concentrated the more times you boil your water. But! and there’s always a but! The amounts are so small, that they’re negligible.
Water should never contain large quantities of nitrates, arsenics and fluoride to begin with. Water suppliers in cities should be monitored to control these levels. So even if you’re getting your water from the tap, it should be safe to drink. For example, nitrates are most commonly found in underground water sources, or in fertilizers. This is not going to be in your city tap water.
If you’re boiling water with high levels of these chemicals, your issue isn’t from twice boiling your water. In fact, when we boil water the chemicals change for the better. It becomes safer for us to drink because it kills off any nasty bacteria or germs that might be in the water.
Most of us are not boiling filtered water exactly for this reason – we simply don’t need to. Anything unwanted in our tap water, will be boiled out. So it’s all about the quality of your water before it was ever boiled in the first place.
Water companies test water, so you can learn about potential issues from them. If you use well water or are concerned about lead from plumbing, you can get your water tested. Keep in mind, reboiling does not significantly increase the concentration of undesirable chemicals already in water. Contaminated source water should be filtered before boiling once, much less twice. Uncontaminated water is safe to boil and reboil.
Reboiling Water May Affect Flavor
Although not a safety consideration, using reboiled water may affect the flavor of coffee or tea. This is because fresh water contains lots of tiny air bubbles. When you heat the water, dissolved gases slightly increase the acidity of water, allowing for a better extraction of flavorful molecules.
Some people also claim boiled water tastes flat. So, it’s best to make coffee or tea with fresh, cold water. It’s a tiny change, so it’s likely very few people can tell whether you used fresh water or whether you reboil water. The quality of the water (its source and dissolved minerals) and the coffee or tea play a much larger role in the flavor of the finished product.
Also, it’s worth noting that the optimal temperature for brewing coffee and tea is below the boiling point of water, so reboiling water might not even enter into the equation.
Generally, there is no health risk if you boil water, let it cool, and reboil it. It’s best if you only reboil water once or twice before starting from scratch.
Reboiling tap water does concentrate minerals and other chemicals in the water. So, if your source water is high in nitrates, arsenic, or other undesirable chemicals, avoid reboiling it.
Similarly, if your water is high in calcium and you have health conditions affected by the mineral, it’s better to avoid reboiling water. It might even be worth switching to distilled or reverse osmosis-purified water. Reboiling pure water does not change its chemical composition at all.