I keep a case of bottled water in my trunk at all times. This has served me well when I make unplanned stops at restaurants to grab a bite to eat. Rather than buying an overpriced and unhealthy soda or sugary drink, I simply grab a bottle of water out of my trunk. I spend about $4 on a case of 24 (including tax but not including CA CRV because I get that back when I recycle the bottles) so each bottle costs me about 17 cents. Much better than paying $1.79 or more for a bottle of water at a restaurant. If you like your water cold, ask for a glass of ice.
I should ad that I do not like the taste of unfiltered tap water which is why I don't order tap water at the restaurant. Many restaurants either don't filter or have what I consider "dirty filter tasting water."