Why it is dangerous to cook with hot water from the tap

Many of us turn the tap to hot water when we want to speed up making soup or pasta. However, experts warn that this seemingly harmless habit can pose serious health risks. Hot water circulating through household pipes dissolves harmful substances from the pipework, and subsequent boiling in the pot only concentrates these contaminants rather than eliminating them.

One important point to bear in mind: unlike cold water, water that passes through heating systems is not subject to the same strict testing standards for food consumption.

What happens inside pipes when water is hot

Prof. Andrew Whelton from Purdue University and chemical engineer Tom Neltner explain the mechanism by which hot water becomes a carrier of toxins:

• Dissolution of heavy metals: the hotter the water, the more rapidly it leaches lead and other metals from pipes, joints, and taps.
• The boiler, a zone of sediment accumulation: boilers act as settling chambers where toxic deposits build up over time. Moreover, the protective anodes inside boilers, manufactured from zinc, are frequently contaminated with lead, which passes directly into the heated water.
• Deterioration of plastic pipes: even modern plastic pipe networks are not entirely safe — hot water accelerates the degradation of the inner surface of the tubing, encouraging the release of microplastics that end up in food.

Why boiling does not solve the problem

A dangerous myth is that hot water becomes safe once it reaches boiling point on the hob. However, nutritionist Dani Dominguez explains that boiling destroys only bacteria and pathogens. Heavy metals such as lead, along with microscopic plastic particles, do not disappear through evaporation — on the contrary, as the volume of water reduces during boiling, the concentration of these contaminants in the food can actually increase.

Four simple rules for a safer kitchen

• Cook only with cold water: fill pots with cold tap water and bring it to the boil directly on the hob or cooker.
• Use an electric kettle: if you want to save time, heat cold water in an electric kettle before pouring it into the pot.
• Let the water run for a few seconds: if the tap has not been used for several hours, let the cold water run briefly before using it, to flush out any stagnant water from the final section of the pipe.
• Clean the boiler regularly: periodically draining sediment from the boiler or central heating system reduces the build-up of metallic deposits and extends the lifespan of the equipment.