Distilled water is neither an acid nor a base. Distilled water has an equal number of hydrogen (positive) and hydroxide (negative) ions, which cancel each other out, making it a neutral.
On the pH scale, distilled water has a pH of 7. The pH scale is used to measure the acidity or alkalinity of a substance. The pH scale ranges from 0 to 14. Numbers less than 7 are acidic, whereas numbers greater than 7 are alkaline, or basic. A substance with a pH of 7 is neutral. Unlike distilled water, most tap water contains other ions, which can make the water either more acidic or more basic.