When an acid is dissolved in water, the pH will be less than 7. When a base, or alkaline, is dissolved in water, the pH will be greater than 7.
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.