Mineral vs spring vs purified water

Bottled water names are legally defined. The same bottle can carry different names in the US and the UK.

United States (FDA)

• Spring water: from an underground formation that flows naturally to the surface. It must be collected at the spring or through a borehole tapping the same formation, and the spring's location must be identified.^[1]
• Mineral water: at least 250 ppm TDS, from a geologically and physically protected underground source, with a constant level of minerals. No minerals may be added.^[1]
• Artesian water: from a well tapping a confined aquifer where the water level stands above the top of the aquifer.^[1]
• Purified water: produced by distillation, deionization, reverse osmosis or similar, meeting the US Pharmacopeia definition. It may also be called "distilled", "deionized" or "reverse osmosis" water.^[1]
• Sparkling bottled water: water that, after treatment, has the same amount of carbon dioxide it had at the source.^[1]
• Water from a community (municipal) system must say "from a community water system" or "from a municipal source", unless it has been treated to meet the purified or sterile definitions.^[1]

United Kingdom

UK law has three categories: natural mineral water, spring water and bottled drinking water.^[2] Natural mineral waters must be officially recognised, and the government publishes the list of recognised waters.^[10] Natural mineral waters can carry labelling indications such as "low mineral content" or "suitable for a low-sodium diet" only when they meet set criteria.^[2]

What this means when comparing

Purified waters (smartwater, Dasani, Aquafina) start from treated water, often municipal, and have very low mineral content. Brands that add minerals for taste say so in their reports. Natural mineral and spring waters keep the minerals from their source, which is why their values vary so much.