You never ever want to use tap water in your car no matter where you are putting it. Use only distilled water. Tap water has too may harsh minerals in it to be used in your car. Distilled water has all chemicals and minerals removed. You don't want to get iron, lead, and lime or calcium deposits in your car from using tap water.
There are varying opinions as to whether or not to use distilled water vs. tap water when changing the anti-freeze in your car. Tap water is not recommended because it causes corrosion and rust, so many reviews suggest a anti-freeze distilled water mix.