pH and Drinking Water

A question often asked is what is the effect of water, with a pH lower than 7, on human health? Under certain conditions a reverse osmosis purifier will lower the pH of the permeate or purified water slightly. (This depends on the equilibrium relationship between CO2, HCO3, and CO3). To understand the effect of pH on water, it is necessary to understand the following: There are strong acids and weak acids, and strong alkalis and weak alkalis.

The pH reading is not indicative of how strong an acid or alkali is, and cannot give any indication of the water quality. Strong acids and alkalis are corrosive, while weak acids and alkalis are non-corrosive. In water an acid or alkali is usually diluted. The pH of stomach juice, which contains hydrochloric acid is between 1 and 3, while commonly used foods like lemon juice and vinegar also have a low pH. They are weak acids though, and pose no health threat to humans or animals. The same applies to carbonated drinks which have a pH between 2 and 4, black coffee with a pH of 5, etc. Millions of people drink these beverages every day.

pH plays an important role in water treatment plants. Water with a low pH has a corrosive effect on metal pipes. It can leach metals like iron, manganese copper and zinc from the plumbing. This can result in water containing high toxic metals, and staining of bathroom and toilet fittings.

Water with a high pH may indicate water which is hard (containing high calcium and magnesium salts) and could form scale which may block pipes, resulting in decreased water flow and the clogging of geyser elements. It can also give water an alkali taste and is bitter when used to make coffee. pH also influences the effectiveness of water disinfectants like chlorine. For chlorine to disinfect effectively the pH must be under 8.

Water with a low pH poses no health threat to humans or animals. Various experiments have been performed to prove this. See De Zuane, J (1990). Handbook of Drinking Water Quality: Standard sand Control. Van Nostrand Reinhold, New York.

Many farmers acidify drinking water to protect their flocks from bacteria. Acidification is also used in laboratories to prevent bacterial contamination among laboratory animals.

The EPA (Environmental Protection Agency) and SANS 241: 2006 Water Standards shed more light on pH. The EPA does not regulate pH. It is classified under the Secondary Maximum Contaminant Levels (SMCL) which is regarded as aesthetic. The EPA recommends water that should have a pH between 6,5 and 8,5.

On pH the World Health Organisation (WHO) says: A direct relationship between human health and the pH of drinking-water is impossible to ascertain, because pH is so closely associated with other aspects of water quality, and acids and alkalis are weak and usually very dilute. However, because pH can affect the degree of corrosion of metals as well as disinfection efficiency, any effect on health is likely to be indirect and due to increased ingestion of metals from plumbing and pipes or inadequate disinfection.

A quote from SANS 241: 2006 on pH: pH: No primary health effect – low pH values can result in structural problems in the distribution system.

Finally: The US EPA has recognised membrane processes such as Reverse Osmosis as a ‘best available technology’ (BAT) for meeting a wide variety of the Safe Drinking Water Act (SDWA) regulations.


  • Wellcare® information for you about pH in Drinking Water.
  • Wikipedia.
  • Free Drinking Water:
  • Government of Saskatchewan: SaskH2
  • Wilkes University Centre for Environmental Quality:
  • SANS 241: 2006
  • World Health Organization: pH in Drinking-water. Revised background document for development of WHO Guidelines for Drinking-water Quality.