Alkaline Water (High pH): Does It Have Any Health Effect?

The pH scale describes the concentration of hydrogen ions: 7 is neutral, below 7 is acidic, above 7 is alkaline. Ordinary tap water and most bottled water sit at roughly pH 6.5–7.5. “Alkaline” water is usually taken to mean pH 8 or higher, although no official threshold defines the term, and the name itself is commercial, not medical.

Three quite different products are sold under one name. The first is natural mineral water whose high pH comes from dissolved bicarbonates, calcium or magnesium picked up on its way through rock. The second is electrolysed water, passed through an ioniser that splits the stream into an acidic and an alkaline fraction. The third is ordinary water with added alkalising drops or tablets, usually based on hydroxides or carbonates. All three can carry the same pH on the label while having very different composition and very different buffering properties.

This distinction is crucial for reading the research. When a paper says “alkaline water lowered a bone-resorption marker”, it usually means bicarbonate-rich water from a specific source, not just any water from an ioniser. Results for one type do not carry over automatically to the others, and a 2026 review in Frontiers in Medicine notes explicitly that the effects are modest and probably depend more on mineral composition than on pH alone.

Arterial blood pH in a healthy person is kept between 7.35 and 7.45. A fall below 7.35 is acidosis, a rise above 7.45 is alkalosis, and deviations of more than a few hundredths of a unit are life-threatening states that need hospital treatment. The body guards this parameter at three levels at once: the chemical buffers of the blood (above all the bicarbonate system), breathing, which removes or retains carbon dioxide within minutes, and the kidneys, which excrete excess acids or bases in the urine over hours and days.

In practice this means that the excess base from water you drink is simply excreted. The only easily measurable consequence is a change in urine pH, which in a healthy person can range from about 4.5 to 8 depending on diet and fluids. A shift in urine pH after alkaline water is therefore real, but it is evidence of the kidneys at work, not of “alkalising the body”. The urine pH strips popular in network marketing show only the urine’s reaction at that moment and say nothing about health or tissue acidity.

Gastric juice has a pH of roughly 1.5–3.5, which is orders of magnitude more acidic than any drinking water is alkaline. The pH scale is logarithmic: one unit of difference means a tenfold difference in hydrogen-ion concentration. A glass of pH 9 water has very little buffering capacity because it contains only trace amounts of alkaline substances. Once swallowed, it mixes with gastric juice, its reaction disappears almost at once, and the stomach carries on secreting acid.

That gives the basic rule of interpretation: what matters for the stomach is not the water’s pH but its buffering capacity, that is, how much acid a litre of that water can neutralise. Capacity depends on the amount of dissolved bicarbonates, carbonates and other bases. A mineral water with several grams of bicarbonate per litre has more buffering capacity than ioniser water at the same or higher pH but with minimal mineral content. That is why judging water by its pH number alone is misleading, and why the studies that found an effect usually involved waters with a defined, high bicarbonate concentration.

The argument most often cited in favour of alkaline water concerns reflux. Pepsin, a protein-digesting enzyme, is activated in an acidic environment and damages the mucosa when stomach contents flow back into the oesophagus or throat. In 2012 Koufman and Johnston described laboratory studies in which artesian water at pH 8.8, containing natural bicarbonates, irreversibly inactivated human pepsin and had a greater capacity to buffer hydrochloric acid than two popular bottled waters of ordinary pH.

A test tube is not a stomach, though. The next step, a randomised trial in patients, came only in 2023. In STOMACH STILL, 148 adults with frequent heartburn for at least 6 months and without moderate or severe oesophagitis drank 1.5 litres a day of either bicarbonate-rich mineral water or control water for 6 weeks. The proportion with a meaningful improvement in heartburn was 84.7% in the bicarbonate-water group versus 63.5% in the control group (p=0.0035), and the number needed to treat for one person to benefit beyond the placebo effect was 5.

How should this be weighed? STOMACH STILL is the best evidence so far, but it is one trial of one water, co-run by the manufacturer. A 2024 systematic review (D’Souza et al.) covered earlier trials of mineral waters for heartburn: nine studies, including three randomised ones of poor methodological quality, and the authors concluded that on this basis drinking mineral waters for heartburn can be neither recommended nor discouraged. The reasonable summary is therefore: bicarbonate water may ease heartburn in some people, but it is not a drug and does not replace treatment of reflux. You can read more about the condition in the gastro-oesophageal reflux entry in our knowledge base.

The second popular promise concerns bones. The ‘acid-ash’ hypothesis assumes that a diet rich in protein and grains and low in potassium creates an acid load that the body neutralises by leaching calcium from bone, which over time leads to osteoporosis. Any benefit of alkaline water is derived from exactly this logic: alkaline minerals would spare the skeleton.

The data are mixed. The 2009 meta-analysis by Fenton et al., restricted to the methodologically best calcium-balance studies, showed that a rise in net acid excretion increases urinary calcium but does not change whole-body calcium balance or the bone-turnover marker (N-telopeptides). The authors conclude that promoting an alkaline diet to prevent calcium loss is not justified. A more recent meta-analysis of RCTs (Han et al., 2021) found that acid-forming diets had no significant effect on bone-turnover markers or bone mineral density, whereas alkaline supplements reduced urinary calcium and the resorption marker NTX, and bone density at the femoral neck and lumbar spine was slightly higher, with the caveat of high heterogeneity in some results and the need for confirmation in larger trials.

A cautious but honest conclusion: there are signs that bicarbonate-rich water may slightly reduce bone resorption as measured in blood tests, but there is no evidence that this lowers fracture risk, or that ordinary high-pH water without a large bicarbonate content does the same. If your bones matter to you, far better-documented measures are adequate calcium and protein intake, vitamin D and resistance training. We cover the disease itself in the osteoporosis entry.

One of the most-cited studies on hydration with alkaline water concerns blood viscosity. In the 2016 study by Weidman et al., a hundred healthy adults exercised in the heat until they had lost about 2% of body mass, then received either electrolysed high-pH water or ordinary purified water in an amount equal to 2% of body mass. After exercise-induced dehydration, high-shear blood viscosity fell by an average of 6.30% after alkaline water and 3.36% after ordinary water (p=0.03).

Proportions matter when judging this result. The other measured markers (osmolality, bioimpedance, body mass) showed no difference, and the one that did is a rheological marker whose clinical meaning in healthy people has not been established. There is no evidence that the difference translates into performance, well-being or the risk of any health event. Moreover, rehydration after exercise rests primarily on drinking an adequate volume and replacing sodium. On that point we refer you to our articles on electrolytes during training and on drinking water after a workout.

In the general population alkaline water is usually well tolerated, but some groups should be careful with it. The 2026 review lists people with chronic kidney disease, those taking drugs that suppress stomach acid, pregnant women and children as populations in which caution is warranted and such water should not be treated as a routine part of the diet.

A separate matter is heartburn that does not go away. Water is not the right tool for diagnosing or treating alarm symptoms. If heartburn comes with difficulty swallowing, pain on swallowing, unintentional weight loss, persistent vomiting, vomiting blood, black stools or anaemia, it needs urgent medical investigation, not experiments with water. The same applies to new reflux symptoms after the age of 50.

The economic calculation is simple: if you occasionally have heartburn and bicarbonate water helps, it may be a reasonable addition to your lifestyle (smaller portions, no eating right before bed, less alcohol and fatty meals). If you have no symptoms and are buying it in the hope of a ‘detox’, ‘de-acidification’ or a longer life, you are paying for a promise that no reliable study confirms.

Alkaline water is a good example of a product in which a grain of truth has been wrapped in a thick layer of marketing. The grain is bicarbonate: in the right amount and form it can ease heartburn and probably has a slight effect on bone turnover. The marketing is everything else: ‘de-acidification’, immunity, slower ageing. If you do buy such water, do it knowingly, with expectations matched to the evidence, and look at the composition, not at the pH figure.