Alkaline Water: What the Evidence Says About the Health Claims

Alkaline water is simply water with a pH above 7, the neutral point. The evidence that drinking it improves health is thin. A systematic review in BMJ Open found no evidence for or against alkaline water in preventing or treating cancer and concluded that promoting it for that purpose “is not justified.” A few small studies on acid reflux and exercise recovery report modest effects, but they have real limits. Regular tap water in the US is meant to sit between pH 6.5 and 8.5, and EPA set that range for taste and pipe protection, not because of any health benefit.

Here is what pH means, where the claims come from, and what the research does and doesn’t show.

What pH actually measures

pH is a scale from 0 to 14 that describes how acidic or basic (alkaline) water is. According to the US Geological Survey, 7 is neutral, values below 7 are acidic, and values above 7 are basic.

The scale is logarithmic. USGS explains that each whole number is a 10-fold change, so water at pH 5 is ten times more acidic than water at pH 6. That’s why a jump from pH 7 to pH 9 is a bigger chemical difference than it sounds.

For context, USGS notes that normal rain has a pH of about 5.6, slightly acidic because of carbon dioxide in the air. Water picks up minerals as it moves through rock and soil, which often pushes its pH up.

What pH tap water is supposed to have

EPA lists pH among its secondary drinking water standards, with a recommended range of 6.5 to 8.5. Secondary standards are voluntary guidelines for things like taste, odor and appearance. EPA does not enforce them, and they aren’t based on health risk.

EPA describes what happens outside the range:

Below 6.5 (acidic): a bitter, metallic taste and corrosion of pipes.
Above 8.5 (alkaline): a slippery feel, a soda-like taste, and mineral deposits.

The corrosion point is the one that matters most for health, and it cuts the opposite way from what alkaline marketing suggests. Acidic water can dissolve lead and copper from household plumbing. That’s why many utilities deliberately adjust pH as part of corrosion control, a topic covered in our guide to how tap water is treated.

The World Health Organization takes a similar view. Its pH fact sheet says no health-based guideline value is proposed for pH, and WHO treats pH as an operational factor that affects how well treatment and corrosion control work.

Your body controls its own pH

The central claim behind alkaline water is that it can make your body “less acidic.” Human physiology doesn’t work that way.

Normal blood pH stays in a narrow band of about 7.35 to 7.45, according to the NIH’s StatPearls reference. The body holds it there using chemical buffers in the blood, the lungs (which remove carbon dioxide) and the kidneys (which excrete acid). Blood pH outside that range is a sign of illness that needs medical care, not something a drink is meant to fix.

The stomach is also highly acidic by design. NIH’s StatPearls notes that pepsin, the main protein-digesting enzyme, works best at a pH of roughly 1.5 to 2. Water you drink mixes with that acid before it goes anywhere else.

The BMJ Open review (Fenton and Huang, 2016) summarized the research this way: diet changes can change urine pH but do not change blood pH. In one trial it cited, a diet change moved blood pH by only 0.014 units while urine pH rose by about 1 unit. Alkaline water may make your urine more alkaline. That isn’t the same as changing the pH of your body.

Claim 1: Alkaline water prevents or treats cancer

This is the most serious claim and the one with the clearest answer.

Fenton and Huang searched published and unpublished research for any study of dietary acid load or alkaline water and cancer. Out of more than 8,000 citations, only one study met their criteria, and it found no link between dietary acid load and bladder cancer. They found no human studies of alkaline water and cancer at all.

Their conclusion: “Promotion of alkaline diet and alkaline water to the public for cancer prevention or treatment is not justified.”

It’s worth being precise. The review found an absence of evidence, not proof that alkaline water does nothing. But a health claim needs evidence behind it, and for cancer there is none. Anyone being treated for cancer should talk with their oncology team before relying on any product sold with this claim.

Claim 2: Alkaline water helps acid reflux

This claim has a real scientific starting point, though it’s narrow.

Pepsin, the stomach enzyme, can damage the throat and voice box when it travels upward in a condition called laryngopharyngeal reflux (LPR). Lab research by Koufman and Johnston, published in 2012 in Annals of Otology, Rhinology & Laryngology, reported that water at pH 8.8 could inactivate human pepsin in a test tube. That’s a lab finding about an enzyme, not a clinical trial in patients.

The main clinical study is a 2017 paper by Zalvan and colleagues in JAMA Otolaryngology–Head & Neck Surgery. It compared 85 patients treated with a proton pump inhibitor (a common reflux drug) to 99 patients who used alkaline water plus a mostly plant-based Mediterranean-style diet and standard reflux precautions. After six weeks, the diet-and-water group did about as well as the drug group on a symptom questionnaire.

Three limits matter:

It wasn’t randomized. Patients were assigned based on when they enrolled.
Alkaline water was bundled with a major diet change, so the study can’t separate the effect of the water from the effect of the diet.
It measured symptoms, which people report themselves.

The study suggests a dietary approach may be a reasonable option to discuss with a doctor for LPR. It doesn’t show that alkaline water on its own treats reflux. If you have ongoing reflux symptoms, see a doctor before swapping out prescribed medication.

Claim 3: Alkaline water hydrates better or improves exercise performance

A 2016 randomized, double-blind trial in the Journal of the International Society of Sports Nutrition (Weidman and colleagues) had 100 healthy adults exercise in heat until they lost about 2% of their body weight, then rehydrate with either high-pH electrolyzed water or standard purified water.

Results were mixed. One measure of blood viscosity (thickness) fell by 6.3% with the alkaline water versus 3.4% with standard water. But the authors found no difference in plasma osmolality, body mass change or bioimpedance, the more standard markers of hydration. The study was funded by Essentia Water, which also supplied the alkaline water, and one author reported consulting fees and stock options from the company. The authors state the company wasn’t involved in data collection or analysis.

Other small studies have looked at mineral-based alkaline water in athletes, mostly measuring acid-base markers during intense exercise. These are short trials in small groups and don’t establish a general hydration or performance benefit for everyday drinkers.

The practical takeaway: drinking enough water matters far more for hydration than the water’s pH.

Is alkaline water harmful?

For most healthy people, drinking alkaline water isn’t known to be dangerous. Water above pH 8.5 can taste like baking soda and leave deposits, which is why EPA’s aesthetic range stops there.

A few cautions are reasonable:

Kidney disease or medications that affect electrolytes. Some alkaline waters have added minerals. If you have kidney problems or a condition that affects your acid-base or electrolyte balance, ask your doctor first.
Cost. Bottled alkaline water and home ionizer machines cost far more than tap water, without demonstrated health payoff.
Infant formula. Use the water your pediatrician recommends. See our guide to tap water for baby formula.

What matters more than pH

If you’re wondering whether your water is healthy, pH is rarely the place to start. The contaminants with real health effects, like lead, nitrate, arsenic and PFAS, don’t show up in a pH reading.

Better steps:

Look up your utility. Search your ZIP code to see your water system’s grade and EPA compliance record.
Read your Consumer Confidence Report. It lists what your utility detected, and many include pH. Our guide to reading your water quality report explains how.
Check your plumbing. Lead comes from pipes and fixtures, not the treatment plant. See how to test and protect against lead.
Filter for a specific problem, not pH. If you want a filter, choose one certified for the contaminant you’re worried about. Our NSF certification guide explains what each standard covers.

Bottom line

pH is a useful number for water utilities because it affects taste and pipe corrosion. As a health intervention, alkaline water has very little evidence behind it. There are no human studies supporting cancer claims, the reflux evidence is limited and tied to diet changes, and the hydration research shows small, mixed results from an industry-funded trial. If you enjoy the taste, it’s generally fine to drink. If you’re buying it for a health reason, talk to your doctor and spend the effort on what actually affects water safety.