Water filtration could be important for your dog. If you are concerned about the quality of your water, even the simplest of filters may help remove fluoride, for example. Larger and more complicated systems may be needed to filter out pharmaceuticals, asbestos, or other particles.
To check on the safety of your water supply in the UK, go to https://www.gov.uk/check-drinking-water-quality. Always use water and food bowls made of metal or ceramic, not plastic, which can carry its own chemical signature.