What's Really in Your Water? Tap, Bottled and Forever Chemicals
Every day, without a second thought, we turn on the tap. We fill a glass, boil the kettle, make a cup of tea (many cups, in my case). We assume that what flows out is simply water.
It is a little more complicated than that, and a great deal more interesting.
Our water carries traces of the lives we lead: the medicines we take, the cosmetics we wear, the dyes in our clothes, the flame retardants in our sofas. And water does not stop at borders. It moves through rivers, rock and rain, from one country to the next, and eventually around the planet.
To follow that journey, I was joined by Professor Emma Schymanski, Head of Environmental Cheminformatics at the Luxembourg Centre for Systems Biomedicine at the University of Luxembourg and an FNR ATTRACT Fellow. Her work combines cheminformatics with high-resolution mass spectrometry to identify the unknown chemicals hiding in water samples, and to trace them back to where they came from.
A fingerprint of how we live
When Emma's team analyses a sample, they are reading a record of everyday human life.
“We can see what people are wearing. We can see the medication that they're taking.” Professor Emma Schymanski
Pharmaceuticals, cosmetics, clothing dyes, flame retardants and pesticides all leave their signature. Even differences in national regulation show up. Emma's team found much larger traces of flame retardants in UK house dust than in the EU, a reflection of Britain's stricter fire-safety rules for furniture. It is a genuinely difficult trade-off. Nobody wants a fire, yet a chemical that is everywhere is a chemical we are all exposed to.
“For us it's a big fingerprint that tells you a lot about life, in a way.” Professor Emma Schymanski
Almost no water is untouched
When Emma first came to Europe from Perth, researchers could still hope to find pristine reference sites: clean samples to measure everything else against. That is becoming almost impossible.
“It's getting more and more difficult to find water that hasn't got any form of traces.” Professor Emma Schymanski
Contamination that begins in America can travel around the globe and fall as rain in the most remote places. It is being found in the Arctic and in Antarctica. As Emma reminded me, it is not just a water cycle, it is a complete cycle, and the air is part of it.
Where Luxembourg's water comes from
In Luxembourg, around half of our drinking water comes from the lake at Esch-sur-Sûre and half from groundwater. It is abstracted, treated, monitored and tested before it reaches our taps. Under EU rules, every member state must monitor a list of priority pollutants, along with pollutants specific to each river basin, and report the results.
Some of that vigilance was born of disaster. In 1986, an industrial accident in Switzerland turned the Rhine red and killed its fish. Today the river is analysed every day in Basel, so that cities downstream, such as Stuttgart, can be warned before a problem reaches their drinking water.
Why warm water tastes worse
Treatment is not only about chemicals. It also protects us from microbes and the diseases they carry. Luxembourg's water supply sits at around 10 degrees, so relatively little disinfection is needed. In Perth, where Emma grew up, water in the supply chain can rise above 27 degrees, and far more disinfectant is required to keep it safe. That is why tap water in hotter countries often tastes noticeably worse.
Drawing the line on risk
Treatment aims to bring contaminants below a level of concern, rather than to remove every last molecule. Where that line sits is one of the hardest things to explain to the public. Emma once worked on a contaminated site in Perth where the threshold was set at a risk of one in a million. Residents pointed out that Perth is a city of 1.5 million people. It was a fair point, and also a reminder that cleaning the site any further would have been technically and financially out of reach.
One simple habit
The most practical advice of our conversation was also the simplest. Water that has been sitting in your pipes is not the same as water fresh from the supply, particularly in older homes. So let the tap run until the water turns cold.
“I would recommend you run your water into a watering can, and at least put that water on your garden afterwards, because your garden will not complain.” Professor Emma Schymanski
Emma does exactly this every morning. And her reassurance matters just as much as her advice.
“The water that is actually being distributed to you is very good quality.” Professor Emma Schymanski
Also in this episode
We also explored whether bottled water is genuinely safer than tap, what happens to medication after it leaves our bodies, how wastewater can reveal changes across a whole population, why PFAS forever chemicals are so hard to regulate, whether household filters help, and how much water AI data centres consume.
I would love to know: do you normally drink tap, filtered or bottled water?
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