česma

1. (outdoors, in a park) public drinking fountain
   Napunili smo flaše na česmi u parku. — We filled our bottles at the fountain in the park.
   U selu je stara česma ispred crkve. — In the village there's an old fountain in front of the church.
2. (in the home) tap; faucet
   Pijem vodu sa česme, ne kupujem flaširanu. — I drink tap water, I don't buy bottled.

"Voda sa česme" is the usual way to say tap water. Both česma and slavina are everyday words for a tap; slavina more often refers to the fixture itself (the one that drips or gets replaced).