In the United States (and I believe most other modern countries), you do not need to pay for water from restaurants. It's considered a basic human need. However, some places will instead charge you for the cup, or the ice they put in it. Once a place tried to pull this on me, so I asked if I could just hold my mouth under their sink and drink that way. They gave it to me for free.
Similarly, bottled water. Drink from the tap or if the water quality's bad buy a purifier, bottled water is ridiculous.
Or get your water from restaurants.