Almost every conversation about drinking water is about what should not be in it. There is a shorter, less familiar conversation about what should.
The published position
WHO-convened expert reviews have looked specifically at demineralised water and set out minimum desirable levels for calcium and magnesium, on the grounds that water is a meaningful contributor to intake and that very low-mineral water may be undesirable for long-term consumption.
The reasoning is straightforward. Minerals dissolved in water are absorbed readily and require no digestion. It is a small, passive, reliable contribution — and it is switched off entirely when the water is demineralised.
What each one does
- Calcium — bones, teeth, muscle contraction and heart rhythm. Adults need in the region of 1,000 mg a day. Mineral-bearing water can contribute 40–150 mg.
- Magnesium — muscle and nerve function, energy metabolism. Requirement is roughly 300–400 mg a day, and this is the one Indian diets most commonly fall short on. Water can supply 20–80 mg.
- Potassium and sodium — fluid balance and how quickly water is absorbed rather than sitting in the stomach.
- Bicarbonates — pH buffering. This is what keeps water at 7.0–7.5 instead of drifting acidic.
But surely food covers it
For most people, largely yes. Food does 85–95% of the work and no one should rely on water as a mineral source.
The point is subtler. You are not choosing between water and food as a source. You are choosing whether to keep a contribution you already had, that costs nothing, requires no behaviour change, and happens roughly thirty times a day without your involvement.
This is general guidance on water composition. Anyone managing a specific condition — kidney disease in particular — should follow their doctor's advice on mineral intake rather than a purifier brochure.
