Why Does My Tap Water Taste Like That? Our Water Taste Scientist Explains

We asked our water taste expert Dr Bill Simpson your burning questions on the common tastes and smells of tap water. And his answers might just surprise you.

Why does my tap water sometimes smell like a swimming pool?

That faint chlorine smell is actually a sign things are working as they should. Chlorine is what's been keeping your water safe since it was first introduced around 110 years ago - before that, drinking tap water was genuinely risky. The goal is just enough chlorine to do the job, not so much that you notice it.

The challenge is that your neighbour one mile from the treatment works gets more chlorine in their water than you do three miles away, simply because it breaks down along the way. Water companies also sometimes switch between chlorine and a compound called chloramine - more stable, travels further, but slightly more noticeable in smell. One day nothing, the next day swimming pool. That's not something going wrong. That's just the system doing its thing. And if you'd rather not taste it? A filter takes it out entirely.

Why does my tap water taste different from one day to the next?

Sometimes it's the water. Sometimes it's you. Professional taste panels sit down with ten identical water samples and still find differences between them - so even the experts aren't immune.

First thing in the morning, you're drinking water that's been sitting still in the pipes overnight. By afternoon, after everyone's made their tea and coffee, it's been moving more freely. Flow rate changes chlorine levels, which changes taste. Your own senses shift too - with age, medication, illness (COVID being a dramatic recent example).

And if you've ever visited someone fifty miles away and found their tap water tastes completely different? It does. Water is a local product. It reflects the geology of wherever it came from. That's not a flaw. It's just how water works.

Why does my tap water taste worse in summer?

Warmer pipes mean slightly more microbial activity - mostly harmless, occasionally noticeable. Summer water can taste subtly different for that reason.

There's also something called thermal taste: about one in five people experience a shift in how water tastes simply because the temperature has changed. Same water, different temperature - suddenly it seems more bitter, or metallic, or slightly sweet. Nothing wrong with the water. Just something interesting about how taste works.

My tap water has a metallic taste. Should I be worried?

Often it's not the water at all. Temperature changes alone can trigger a metallic sensation in some people - a kind of phantom taste response. Amalgam fillings, certain foods (particularly oily fish eaten just before), and even what's in your saliva can all play a part.

When it is the water, iron is usually the culprit. The pipes delivering water to your home - especially inside older properties - can introduce trace iron along the way. Interestingly, iron itself is tasteless. What you're actually detecting is a compound called epoxydecanal, which forms when iron reacts with fats in your mouth. It's the same compound that gives blood its metallic smell. If you suspect the pipes in your home are the source, try running the tap for a minute first - you'll often flush it straight through.

My tap water has a damp, earthy smell. What's causing it?

This one usually traces back to tiny amounts of bacteria or mould growing in pipes where there's a small air pocket above the water. The compound responsible - geosmin - is so potent that even a nanogram per litre (that's one-billionth of a gram) is enough to notice. You might also encounter it when water is drawn from open lakes, particularly in summer, where blue-green algae produce the same compound. It smells faintly of beetroot. Carbon filtration removes it very efficiently.

What does genuinely good tap water actually taste like?

The absence of anything to notice. You pick up a glass, drink it, and think about something else entirely. Good water doesn't ask to be thought about. When you find yourself wondering what is that?- a coating feeling, an aftertaste, something vaguely antiseptic - that's when you know it could be better.