Turning the mixer towards hot to fill the pasta pot or kettle more quickly, many do it without thinking about it. A French microbiologist points out, however, that cooking with hot tap water is not just a time saver, but an action that can expose the whole family to very real risks. Behind this detail lie quite concrete chemical and microbiological problems, especially in cooking. Christophe Mercier Thellier, microbiologist and hygienist, then author of the book Hygiene is health! reveals everything in the columns of Our Time.
Why is hot tap water not suitable for cooking?
Christophe Mercier Thellier sums up the situation as follows: “Is tap water still safe to drink? Cold water, normally yes. The municipality undertakes to provide you with consumable water and warns you if there is chemical pollution.“, he explains. Once past the meter, the water circulates in a tank, sometimes old pipes, then a more or less scaled tap, without systematic health checks.
The Ministry of Health reminds that domestic hot water is not considered drinkable. Pipes and some equipment can release lead, copper or nickel. “The dissolution of metals in water can be increased by prolonged stagnation of water in internal pipes and the possible presence of a collective or individual water softening device.“, he specifies. These heavy metals are associated with neurological, renal, cardiovascular disorders or certain cancers.
Heavy metals, bacteria…
The risks are not just organic. Water that remains lukewarm in a tank can accumulate rust, lime deposits, sediments and micro-organisms. According to Christophe Mercier Thellier, “Some outdated balloons do not heat above 50 degrees, but many micro-organisms survive at this temperature, warns the specialist. And even at 60 or 65 degrees, we still find germs, including bacteria!“.
The expert also recalls: “Certain bacteria have the ability to surround themselves with a shell that allows them to resist very high temperatures.” And “even in boiling water, there are certain bacteria that can cause illness“. Possible result when drinking or cooking with this hot water: “You could suffer from nausea, vomiting, diarrhea if certain bacteria attack your digestive system“. He also quotes “Among these bacteria which survive in extreme conditions and are harmful, we will find legionella, responsible for legionellosis.“, a rare but serious lung infection.
Good reflexes for cooking safely
For the hygienist, the precautionary principle is clear: “because no one is able to assure us that it is drinkable”. He recommends using cold water exclusively for drinking, preparing tea, coffee, soup, pasta, rice or baby bottles, before heating it in a kettle or saucepan. Hot water, she, “is made for showering and washing dishes, but certainly not for drinking!“. It is also better to avoid rinsing vegetables or toothbrushes in hot water and let a tap run for a few moments if you have not used it for a long time.
Christophe Mercier Thellier finally recommends unscrewing and regularly cleaning the faucet aerator: “Because tartar is an aggregate of calcium carbonate, dirt, microorganisms, etc.“. As for cold water, specialists recommend keeping it in a carafe in the refrigerator in a clean, closed glass container, and generally consuming it within 24 to 48 hours. Enough to rethink every pot that you are about to fill too quickly with hot water.