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Water pH and Hardness

The pH of Drinking Water

The water with pH 7 is neutral (such as distilled water), below pH 7 is acidic and above pH 7 is alkaline. The United States Environmental Protection Agency (EPA) has established The Secondary Maximum Contaminant Level (SMCL) for pH of drinking water between 6.5-8.5 [1]; there are no known benefits or dangers of drinking water with pH within this range.

Acidic Water

Acidic water (pH <6) may leach toxic metals, such as lead and copper, from pipes and cause metallic or bitter taste in mouth [2].

Carbonated water pH is 3-4 [3]. Carbonated water may cause transient bloating in some people but other than that it has no known side effects; it does not seem to increase the risk of gastric ulcer, kidney stones [4] or osteoporosis [6]. It also does not seem to have any special health benefits. Carbonation does not make water 100% sterile but kills many bacteria, so it is considered safe to drink for travelers in areas with increased risk of food poisoning [5].

Ambiental rainwater is usually acidic due to dissolved carbon dioxide (CO2), sulfates and nitrates from the air, and its pH may be as low as 4-5.5 [7]. The pH of harvested rainwater may range from 5.5 to 8.7, depending on the roof or tank materials [176].

Alkaline Water

Alkaline water at pH >8 may have a soda-like taste.

Most tap water has pH between 6.5 and 8.5 [18], but some municipal water suppliers may raise the pH of water to 9 to prevent plumbing corrosion [174]Hard water, which is high in calcium and/or magnesium, is usually more alkaline than soft water.

There seems to be no convincing evidence about health benefits or dangers of drinking alkaline water [8].

Drinking water can be made:

  • more alkaline by adding baking soda, soda ash, potassium carbonate, sodium hydroxide, calcite or lime or calcium carbonate, or magnesium oxide
  • more acidic by adding white vinegar or acetic, citric, nitric, hydrochloric, sulfuric or phosphoric acid [10].

Hardness of Drinking Water

Water that contains high amounts of calcium and/or magnesium is considered hard, and water with low amounts is soft. Water hardness is determined by the level of calcium carbonate in water (in milligrams per liter) [11]:

  • Soft = 0-60 mg CaCO3/L
  • Moderately hard = 61-120 mg CaCO3/L
  • Hard = 121-180 mg CaCO3/L
  • Very hard >180 mg CaCO3/L
  • The US water hardness map

Benefits and Dangers of Hard Water

Magnesium usually contributes only up to 10% to water hardness [12]. According to some reviews of studies, water hardness is considered neither harmful nor beneficial for health [12,15]. It is not clear if hard water increases the risk of kidney stones [15]. Mineral waters with very high magnesium content can have a mild laxative effect and may help relieve constipation in some people [16].

Drinking water contributes a relatively small amount of calcium and magnesium: two liters of hard water contains about 120 mg of calcium (the Recommended Daily Allowance (RDA) for calcium is 1,000 mg/day [13]) and up to 52 mg of magnesium (the RDA for magnesium is 400 mg/day [14]).

Water Scams

Ionized Alkaline Water

There are no machines (“water ionizers”) that could make drinking water ionized or significantly alkaline by electrolysis. Water alkalinity comes from dissolved minerals, mainly calcium and magnesium and not from electric current applied to water. When you ingest alkaline water it gets neutralized by stomach acid. Further, in the small intestine either acidic or alkaline water becomes alkaline because of the presence of alkaline pancreatic juice. Contrary to false claims, alkaline water is not antioxidant but oxidant. Health benefits of naturally alkaline (hard) water have not been proven. Alkaline water may slightly reduce the acidity of the stomach but there seems to be lack of studies that would confirm beneficial effects of alkaline water on gastroesophageal reflux disease (GERD). Alkaline water also does not treat acidosis (low pH of the blood). The pH of the blood cannot be changed by alkaline diet but by removing excessive acids or bases by breath and urine.

Reference: [9,17]

Acidic Water (H30)

Some producers sell “acidic water.” But carbonated water and rainwater is also acidic. Acidic water cannot treat alkalosis (high pH of the blood). There are no known health benefits of acidic water [17].

Hydrogen Rich Water

Some producers sell “hydrogen rich water” or “reduced water” with added “active hydrogen,” like “H4O hydrogen bonded water” [17]. Added hydrogen can be kept in the water only when under pressure, just like CO2 in carbonated water. Most of H2 would be removed from “hydrogen bonded water” quickly after opening the bottle, though [17].

Oxygenated Water

The same way as hydrogen, most of the added oxygen is removed from water as soon as you open the bottle. You get oxygen by breathing. There are no known health benefits of oxygenated water [17].

Energized Water

There is no scientific proof that beneficial energy of any kind could be added to pure water [17].

  1. 2013, Secondary Drinking Water Regulations: Guidance for Nuisance Chemicals  United States Environmental Protection Agency
  2. Oram B, Drinking Water Issues Corrosive Water (Lead, Copper, Aluminum, Zinc and More)  Water-Research Center
  3. Jay JM et al, 2005,  Modern Food Microbiology
  4. Saldana TM et al, 2012, Carbonated Beverages and Chronic Kidney Disease  PubMed Central
  5. Diemert DJ, 2006, Prevention and Self-Treatment of Traveler’s Diarrhea  PubMed Central
  6. Tucker KL et al, 2006, Colas, but not other carbonated beverages, are associated with low bone mineral density in older women: The Framingham Osteoporosis Study  American Journal of Clinical Nutrition
  7. Acid rain United States Environmental Protection Agency
  8. Zeratsky K, Is alkaline water better for you than plain water?  Mayo Clinic
  9. Alabama Cooperative Extension system
  10. Metzger MR, 2008, Jar Testing for pH and Alkalinity Adjustments  Water Conditioning & Purification Magazine
  11. Water Hardness and Alkalinity  U.S. Geological Survey
  12. Fawell JK et al, 2006, Hardness in Drinking-water   World Health Organization
  13. Calcium  Linus Pauling Institute
  14. Magnesium  Linus Pauling Institute
  15. Sengupta P, 2013, Potential Health Impacts of Hard Water  PubMed Central
  16. Dupont C et al, 2013, Efficacy and Safety of a Magnesium Sulfate–Rich Natural Mineral Water for Patients With Functional Constipation  ScienceDirect
  17. Lower S, “Ionized” and alkaline water  Chem1.com
  18. The pH of water  Water-Research Center

4 Responses to "Water pH and Hardness"

  1. Agnes says:

    Is hard water good for washing hair..? If not what should b the ph of water to wash hair?

    • Jan Modric says:

      Water hardness as such should not be a problem, because neither water nor the calcium from water remain in the hair once they dry off. Water hardness might affect how well the shampoo mixes with water.

  2. mara says:

    “When you ingest alkaline water it gets neutralized by stomach acid. Further, in the small intestine either acidic or alkaline water becomes alkaline because of the presence of alkaline pancreatic juice.”

    Does this quote also apply if you are drinking large quantities of water seeing as the pancreatic juices will be diluted?

    I have purchased an alkaline water filter which uses rocks to mineralize and alkalize the water. Does drinking this water offer any health benefit at all?


    • Jan Modric says:

      Mara, if the water is not neutralized in the stomach or small intestine, it will be neutralized at least when it comes into the blood. The human body has a strong buffering capacity, so everything with high or low pH will be quickly changed into normal pH of the body fluids.

      If the pH of the pancreatic juice in the duodenum gets diluted or the pH of the mixture of all juices there increases or decreases, the pancreas will quickly adjust and start to produce juice that will result in appropriate pH in the duodenum.

      Some people think that drinking alkaline water can neutralize the stomach acid to the point that it can help in acid reflux. But acid reflux is not about stomach acidity but about excessively relaxed muscle sphincter at the bottom of the esophagus, which allows the leak of acid into the esophagus.

      After the research I’ve made so far, I didn’t find convincing evidence about health benefits of drinking alkaline water.

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