Tap water is mostly water plus dissolved minerals – mainly calcium, magnesium and trace salts picked up from the rock it passed through. Depending on region and pipework, it can also carry chlorine from treatment, small amounts of metals such as iron or copper, and trace substances modern analysis detects at very low levels. The exact profile varies by region, which is why suppliers publish local water-quality data.

Yes – UK tap water is safe to drink and among the most rigorously tested in the world. Suppliers test samples continuously against strict legal standards, and results are published by region. Filtration is not a safety requirement: most people filter for taste, less limescale and better tea and coffee – not because tap water is unsafe.

Water hardness describes how much dissolved calcium and magnesium your water carries. Rain collects both as it passes through limestone or chalk, so hardness depends on regional geology. Hard water is safe to drink – the practical effects show up elsewhere: more limescale when water is heated, and a different taste in hot drinks. Your supplier lists the hardness level for your area.

A household water filter changes the composition of tap water – mainly by reducing carbonate hardness and substances that affect taste, such as chlorine. Inside the cartridge, ion exchange swaps out part of the calcium and magnesium, while activated carbon binds taste-affecting substances. The result is not "purer" water in a medical sense; it is water with less scale potential and a cleaner taste.

Tap water tastes different because its mineral profile reflects local geology. Water that passed through chalk or limestone carries more calcium and magnesium and tastes fuller; soft water from granite regions tastes lighter, sometimes flatter. Treatment plays a role too – chlorine levels vary, and older pipework can add its own note. Same standards, different character.

Most adults need roughly 1.5 to 2 litres of fluid a day – most guidance suggests six to eight glasses. The right amount varies with body size, activity and weather, and food contributes part of it. For healthy adults, thirst is a reasonable guide. All non-alcoholic drinks count towards the total; water is simply the most direct choice.

No – boiling and filtering do different jobs. Boiling kills microorganisms but does not remove hardness minerals; as water evaporates, the scale stays behind in your kettle. Filtration with ion exchange reduces carbonate hardness before heating, so less scale forms in the first place. Where tap water is safe, boiling adds little – filtering changes taste and scale, boiling changes neither.