Can you boil water twice?

In this brief guide, we are going to answer the question “can you boil water twice?”, and also bust some myths regarding the effects of reboiling water.

We all have boiled water twice, thrice, many times because it’s easy, saves water, saves energy, saves efforts, and also kills bacteria in the water. But there are many claims that water should not be reboiled as it is harmful and dangerous to health. Is it true? Let’s find out.

Can you boil water twice?

Yes, of course, you can. Reboiling water does not affect our health until the water we drink is safe and of good quality in the first place. It is believed that, when we boil water once, let it cool and reboil it, it concentrates certain undesirable chemicals (nitrates, arsenic, and fluoride). 

These chemical compounds are dangerous only when present in a large amount. Usually,  the drinking water contains these chemicals in a very negligible amount way below permissible limits.

What happens when we reboil water?

When we boil water, it begins to evaporate and a small amount of water is lost to the atmosphere as steam. So now the amount of water left has increased concentration of minerals compared to the normal water before boiling. It is said that the concentration of these minerals increases when boiled twice and so on.

Well, it is true. Experiments show that when water is reboiled it shows two main physicochemical changes: first is water evaporation and the second one is the concentration of unreactive components(dissolved chemicals). Temporary hardness is also reduced during boiling.

But, the change in concentration of dissolved chemical compounds, including those harmful to human health, is very limited even after boiling several times and it does not degrade the quality of water.

Beliefs about effects of boiling water twice: True/ False?

1. Reboiling can increase the concentration of arsenic resulting in cancer, heart disease, and infertility – false

Arsenic is a poisonous chemical that may cause a health risk when consumed 0.6 mg/kg/ day, this would require boiling down 10000 liters of water to fit in one cup. So even after reboiling several times the amount of arsenic is negligible.

2. Water reboiling can increase the concentration of fluoride causing damage to the cognitive and neurological development of children -false

Fluoride is present in the public water supply. It is added to help fight against cavities.

Reboiling water hardly affects the Fluoride concentration. The amount of fluoride to become dangerous is way more than what is present in water in the first place.

3. Reboiling water causes nitrates to become carcinogenic– false

Nitrates are not carcinogens themselves but they have the potential to react with other substances to form nitrosamines (carcinogen). But boiling or reboiling of water has nothing to do with it.

Does boiling water twice change its taste?

Yes, it can taste different. The water undergoes physicochemical changes when boiled. Boiling removes impurities and certain minerals become more concentrated. This change in mineral concentration may cause a change in taste.

The main reason for the difference in taste can be due to the removal of oxygen. Boiling water twice may show a slight change in taste but only if boiled in succession. If boiling is done at intervals then water gets time for oxygen incorporation.

Does using twice boiled water affect the taste of your tea/coffee?

We usually do not drink twice boiled water, instead we use it to brew tea or coffee. So the taste of coffee/tea may not get affected by boiling twice or more. And even if it does, you will not even notice.

Can you drink twice boiled water?

Yes, you can drink water that is boiled twice or even more. Drinking reboiled water does not show any harmful effects on health. Instead, it kills bacteria present in water.


In this brief guide, we answered the question “can you boil water twice?”, and also busted some myths regarding the effects of reboiling water.

As we stated in the beginning, yes you can boil water twice or even more times as long as the water satisfies all sanitary standards in the first place.

Is it safe to boil water twice? Yes, it kills harmful bacteria and removes impurities making it safe to drink.

Harmful chemicals may be present in water and their concentration does increase upon reboiling, but it is very negligible. Their concentration is so minimal that it can not affect our health and will definitely not cause cancer.

Therefore, there is no need to worry about drinking repeatedly boiled water.

You can use fresh water each time if you want,  but if you don’t then also it’s ok. It’s totally safe to boil water twice.

References –

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