Water marketing claims, assessed

Blood pH is held between 7.35 and 7.45 by powerful buffering and by respiratory and renal regulation. Drinking alkaline water cannot shift it — if anything could, that would be a medical emergency rather than a benefit. Stomach acid at pH 1.5 to 3.5 neutralises ingested alkalinity almost immediately.

• Systemic pH is tightly regulated and is not responsive to dietary alkalinity
• "Acidic body" is not a recognised clinical condition; acidosis is, and it has specific pathological causes
• Urine pH does change with diet, which is sometimes presented as evidence of systemic change — it is evidence of the kidneys doing their job

There is a plausible mechanism — a small laboratory study found that water at pH 8.8 irreversibly denatured pepsin, the enzyme implicated in reflux damage — and some small clinical studies report symptomatic improvement. The evidence base is thin and the effect, if real, is local to the oesophagus rather than systemic. This is a narrow, specific claim quite different from the general alkalinity claim above.

Molecular hydrogen dissolved in water is a real thing with a plausible mechanism as a selective antioxidant, and there is a genuine and growing body of small clinical studies. But the studies are mostly small, short and heterogeneous, and dissolved hydrogen escapes quickly from an opened container. The honest position is that this is an open research question, not an established benefit.

Liquid water does form transient hydrogen-bonded clusters, but they rearrange on a timescale of picoseconds. No structure can be imposed on liquid water and persist long enough to be bottled, sold and drunk. The claim describes a state that does not exist outside ice.

Oxygen is absorbed through the lungs, not the digestive tract. The quantity of oxygen that can be dissolved in a bottle of water is a small fraction of what a single breath delivers, and the digestive tract is not an efficient route for oxygen uptake in any case.

For high-mineral waters, yes, measurably. A litre of a water containing 350 mg/l calcium provides a substantial share of an adult daily requirement, and the calcium in water appears to be at least as bioavailable as that in dairy. But this applies only to genuinely high-mineral waters — most bottled waters contain far too little for the contribution to matter.

Glacial water genuinely tends to be low in dissolved minerals, because it fell as snow and had little contact with rock. That is a compositional fact, not a purity claim: low mineral content is not the same as free of contaminants, and glacial meltwater can carry sediment and accumulated atmospheric deposition. "Pure" in this marketing sense means "low TDS", which is a preference, not a quality.

Bottling at source is a legal requirement for natural mineral water in the EU and UK, not a distinguishing feature. Every product legally described as natural mineral water is bottled at source. Presenting a regulatory requirement as a premium attribute is technically accurate and substantively empty.

WHO has reviewed the question and noted that water very low in minerals may have marginally lower palatability, may be slightly aggressive to plumbing, and contributes nothing to mineral intake. In a varied diet, minerals come overwhelmingly from food, so the nutritional point is minor for most people. Municipal RO plants remineralise their product mainly for taste and corrosion control rather than for health.