Over 60% of the water in the UK is described as "hard" or "very hard", which means it has a high mineral content. If, when you pour a glass of water, it looks a little cloudy, then it's likely you live in a hard water area. You might also battle constant white patches on dark work surfaces or tiles and quick build up of scale in your kettle, around taps, and in the toilet bowl. You can do a postcode check if you're still unsure.
Those mineral deposits that build up in your kettle can also build up on your hair, causing it to look flat and dull. Does that mean soft water is better for your hair? In theory, yes. But of course it's not that simple. There is such a thing as "too soft". Very soft water can make it difficult for you to rinse away product build up. If you don't use a lot of hair products, you might not notice, but if you've got oily hair, this can add to the problem.