Vienna is probably one if the safest capital cities in Europe. As a female there is no need to feel threatened if you are walking in the city after dark. If you are travelling by car there are many car park garages that provide parking spaces near exits for female drivers. Unfortunately pickpockets have spread their fingers to Vienna. Beware, always have your wallet packed well away and out of reach, especially when riding a packed underground train or tramway. Also the Prater (amusement park) has been known to have pickpockets, even the Austrians are not safe from them! 

Drinking water from the facets in Vienna is no problem at all. The water comes directly from the mountains and has very good quality, so enjoy it!!!