Drinking warm tap water: is it safe?

Reading time: ~8 minutes

A glass of warm water with lemon in the morning, making tea quickly from the hot tap, or preparing baby food with lukewarm water from the mixer tap: it looks convenient, but it is not a good idea. In the Netherlands only cold tap water counts officially as drinking water. Warm water from the tap does not, and that has everything to do with what gets into the water along the way. In this guide we explain why, what the risks are precisely, and how you can be sure of pure, good-tasting water at home.

What do we mean by warm tap water?

The distinction matters. Drinking water companies supply water that meets strict legal standards right up to your water meter. From your cold tap, that water comes out essentially unchanged. As soon as water enters your hot water circuit, however, it passes through a heater and separate pipes where the water quality is no longer guaranteed. Lukewarm water from the mixer tap counts too: that is partly warm water. At PureFilter we see that many people are unaware of this difference and use the hot tap purely for convenience.

Why is warm tap water not advisable?

Drinking water companies such as Vitens, WMD and Waterbedrijf Groningen, the regional Dutch water utilities, all advise against drinking warm water straight from the tap. There are three main reasons for that.

1. Metals dissolve faster in warm water

This is the most important reason. Metals dissolve more readily in warm water than in cold water. Warm water from your boiler and pipes can therefore contain higher concentrations of copper (from copper pipework and the storage vessel), lead (in older homes with lead pipes), and nickel, zinc, iron, chromium and cadmium (from taps and fittings). Lead in particular is harmful, above all for young children and pregnant women, because it can affect the development of the brain even at low concentrations.

2. Bacterial growth at lukewarm temperatures

Water that stands still for a long time at a lukewarm temperature is an ideal breeding ground for bacteria. According to the RIVM, the Dutch national institute for public health and the environment, the legionella bacterium multiplies best at temperatures between roughly 25°C and 50°C. That is exactly the range the water sits in within parts of a hot water circuit that are lukewarm rather than genuinely hot. Only above 60°C is legionella killed off. Water coming out of the hot tap that has been sitting somewhere in between can therefore contain more bacteria than fresh cold water.

3. Loss of oxygen and flavour

Heating lowers the oxygen content of the water and can change the taste. Warm tap water therefore often tastes flat or slightly metallic. In some systems, unwanted substances such as nitrites can also form during this process. In short, the water loses precisely the freshness you value cold tap water for.

Tap water and temperature: what happens?

Temperature is the key to this whole story. The table below shows what happens to the quality of your water at which temperature.

Worth knowing: cold tap water can also contain slightly more metals if it has stood still for a long time. So let your cold tap run for a moment if no water has flowed through the pipe for more than a week, after a holiday for instance. Half a minute of flushing, until the water feels cool, is usually enough.

Why cold (and filtered) water is better

Cold tap water in the Netherlands is of high quality and meets the legal standards. Even so, cold water can still contain traces of substances that just fall short of exceeding the limit, or that are picked up along the way in your own domestic pipework, such as PFAS, microplastics, pharmaceutical residues and heavy metals. If you would rather be safe than sorry, and want better-tasting water at the same time, filtration on the cold water supply is the answer. Which technique suits you best is explained in our overview of water filter types.

The PureFilter Mineral+ water filter is fitted under the worktop on the cold water pipe, precisely the tap you ought to be using for drinking water anyway. The 5-stage system removes more than 100 contaminants by up to roughly 99 per cent, among them lead, copper, PFAS, microplastics, chlorine and pharmaceutical residues. The filter is NSF-certified to standards 42, 53, 61 and 372. After that, the Swedish Mineral Rock™ adds magnesium, calcium and potassium, so that your water tastes not only pure but also softer and fuller.

Points to watch and common misconceptions

• Warm water with lemon: the morning routine is fine, but draw cold water and heat it in a kettle rather than using the hot tap.
• Tea and coffee: always use cold water that you heat yourself. The hot tap, or lukewarm water from the mixer tap, is not suitable.
• Baby food: never make up formula with warm tap water. Boil fresh cold water and let it cool to the right temperature.
• Faster to the boil: lukewarm water from the mixer tap seems handy because it boils sooner, but the health risks do not make that worth it.
• A Quooker: a boiling water tap with a stainless steel reservoir gives off no metals to the water and is an exception in that respect. Even so, a Quooker removes no PFAS or heavy metals from the water fed into it.

Comparison: warm, cold and filtered water

What can you do yourself?

In practice it is simple. For drinking, cooking and hot drinks, always use cold tap water and heat it yourself. Let the cold tap run for a moment if the water has stood still for more than a week. If you also want to take out the last traces of PFAS, heavy metals and microplastics and have better-tasting water in the house, an under-sink filter is the logical next step.

The PureFilter Mineral+ starts at 149.00 euro including the first filter, and a replacement filter costs 65.00 euro for a whole year, less than one cent per litre. One filter delivers some 15,000 to 20,000 litres of pure water. You install it yourself in 5 to 10 minutes without a plumber, and thanks to 40 days free returns and a 5-year guarantee you run no risk. Not sure which model suits you? Then have a look at our guide to the best water filter.

Frequently asked questions

Conclusion

Drinking warm water straight from the tap is not advisable. In your boiler and pipes, metals such as lead and copper dissolve faster, and at lukewarm temperatures between 25°C and 50°C bacteria grow best. Every Dutch drinking water company therefore gives the same advice: use cold tap water and heat it yourself. If, alongside that basic rule, you also want to take out the last traces of PFAS, microplastics and heavy metals and have fresher water, a filter on the cold water supply provides that extra certainty.