Learn About the pH of Water

Drinking water
Pure water has a neutral pH, although drinking water may be slightly acidic or basic, depending on dissolved mineral content and other trace chemicals. Images by Fabio / Getty Images

Question: What Is the pH of Water?

The pH of water is a value you should know, plus it's good to understand why the actual pH of water might differ from the theoretical value.

Answer: At 25° C the pH of pure water is very close to 7. Acids have a pH less than 7 while bases have a pH greater than 7. Because it has a pH of 7, water is considered to be neutral. It is neither an acid nor a base but is the reference point for acids and bases.

Why Is Water Neutral pH?

The chemical formula for water usually is written as H2O, but another way to consider the formula is HOH, where a positively charged hydrogen ion H+ is bonded to a negatively charged hydroxide ion OH-. This means water has properties of both an acid and a base, where the properties essentially cancel each other out.

H+ + (OH)- = HOH = H2O = water

pH of Drinking Water

Although the pH of pure water is 7, drinking water and natural water exhibits a pH range because it contains dissolved minerals and gases. Surface waters typically range from pH 6.5 to 8.5 while groundwater ranges from pH 6 to 8.5.

Water with a pH less than 6.5 is considered acidic. This water typically is corrosive and soft. It may contain metal ions, such as copper, iron, lead, manganese and zinc. The metal ions may be toxic, may produce a metallic taste, and can stain fixtures and fabrics. The low pH can damage metal pipes and fixtures.

Water with a pH higher than 8.5 is considered basic or alkaline. This water often is hard water, containing ions that can form scale deposits in pipes and contribute an alkali taste.

More About pH

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