What Is the pH of Water, and Why Does It Matter?

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 higher 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.

Is Water Basic or Acidic?

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

The 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.