Why You Should NEVER Reboil Water

Updated: Oct 13, 2020

Tea is one of the most popular beverages in the world, and most often people use kettles to boil water to make tea. But boiling water twice may have dangerous effects...

What Happens When You Reboil Water?

Boiling water once can remove undesirable compounds and gases. Boiled water is perfectly safe, however boiling the water again can actually result in concentrated chemicals such as nitrates, arsenic and fluoride. These chemicals can put you at risk for certain diseases like cancer.

Steaming kettle

What Are Nitrates?

Nitrates are naturally found in the body but are also commonly used in fertilizers and explosives. The bacteria in your mouth and other enzymes in the body can convert these relatively non harmful compounds into nitrites, which can cause harm.

These nitrites can then be converted into nitric oxide (beneficial for the body) or nitrosamines (harmful to the body). Nitrites are used as preservatives in meat because the nitrites react to the proteins, this is what gives meat its pinky reddish colour. Without these nitrites and some other preservatives the meat would turn brown very quickly. (1)

Food producers often add nitrate and nitrite to processed meats because they:

• Prevent bacterial growth

• Add a salty flavour

• Improve the meats appearance

Some people believe a high intake of processed meat increases the risk for cancer because of the nitrate and nitrite consumption. But, the majority of nitrates are actually consumed in vegetables and these are beneficial to keeping the body healthy. (2) (3)

Dangers Of Nitrates

Nitrates and nitrites are essential to our health, but they can be dangerous if they convert into nitrosamines, which are formed when you boil nitrates or nitrites at a high heat.

Nitrosamines are carcinogenic and is the main cause of cancer in tobacco. Because meat producers use nitrates and nitrites as preservatives and the high amount of amino acids (proteins) in meats react and at high heat they are the perfect formula for nitrosamines.

Because vegetables are lower in protein they are less likely to form nitrosamines at high heat even though they also contain nitrates. It is uncommon for people to also cook vegetables at high enough heat.

High nitrate exposure is one of the known conditions to cause methemoglobinemia, also known as 'blue baby disease'. Infants younger than 3 months are the most susceptible to this disease. The nitrates convert into nitrates which in turn bind to the hemoglobin (blood cells) in the body, affecting the way oxygen is transported. This lack of oxygen can make the skin look blue.


Arsenic is commonly thought of as an extremely toxic substance found in things like seafood. However, something you may not know is that underground water is likely to be highly contaminated with inorganic arsenic. People are often exposed to inorganic arsenic when contaminated water is used to to wash and irrigate crops.

Seafood, meat and dairy products can sometimes contain arsenic, but these are generally much less concentrated than groundwater. Organic arsenic found in foods like seafood is less toxic than its counterpart.

Smoking tobacco is another form of exposure to inorganic arsenic because the tobacco plants can absorb inorganic arsenic present in the soil.

During the boiling process of water, the water evaporates and as a result it increases the concentration of arsenic in the water. Common disinfectants like chlorine will not remove arsenic.

If you live in an area that sources underground water for drinking water, it is a good idea to consider using water treatment methods such as reverse osmosis. This treatment method purifies water, removing almost all chemicals in the water. However, this process removes nutrients and minerals from the water which need to be replaced.

Dangers Of Arsenic

Inorganic arsenic is a carcinogenic and is the most frequently found contaminant in drinking water around the world. Ensure you get your water assessed annually by a professional.

Some symptoms of acute arsenic poisoning include:

• Vomiting

• Abdominal pain

• Diarrhoea

• Muscle cramps

• Tingling in limbs

• Nausea

• Abnormal skin changes (e.g lesions)

Common types of cancers caused by arsenic exposure include:

• Bladder

• Liver

• Lungs

• Lymphatic system

• Kidneys

• Prostate

• Skin

Other health effects of arsenic poisoning may include diabetes, cardiovascular disease and sometimes death. Arsenic can also cause adverse effects on pregnancy outcomes and infant health. Higher mortality rates have been associated to the increased risk of multiple cancers, lung disease, heart attack and kidney failure. (4)

There is no definitive treatment for arsenic poisoning, but vitamin E supplements have been used to reduce the effects of arsenic poisoning. There is not enough information to confirm this as a viable treatment however.

Bottom Line

Always use fresh water when boiling water and only boil as much as you need. Boiling water repeatedly can lead to excess exposure of arsenic and nitrates which have many negative effects. This can be easily prevented by always changing the water in the kettle and getting annual checkups for arsenic in your water.

Reverse osmosis can be used to remove contaminants like arsenic but it is not suitable for drinking as the water is stripped of essential minerals and nutrients.

If you think you or someone you know has been exposed to extreme amounts of arsenic or has symptoms of arsenic poisoning, visit a hospital immediately.

Recent Posts

See All