Question

distilled water is neutral but tap water is not?why

Answer 1

distilled water has no free ions to react but tap water is impure and has free ions of the minerals in it which react.
Hope it helps u

Answer 2

A couple of other subtle factors may affect the pH: ... Since dissolved carbon dioxide exists in equilibrium with carbonic acid, it would tend to lower water pH. If you live in an area with comparatively low atmospheric pressure, your tap water might have a lower concentration of C O X 2 , which would favor higher pH.