4. Still Waters Run Deep

Tap water may indeed be "still" -- no bubbles -- but that's not what your server is offering when he queries "still or sparkling?" The mark-up on bottled water is easily 200%, so going bottled can be as much of a rip-off as ordering a cocktail. Industrywide, bottled water pulls in $200 to $350 million in profits annually, according to Clark Wolf Company, a restaurant consultant. In stores, a 33.8-ounce flat Voss Mineral Water goes for $3.49; in Riingo, located in New York's Alex Hotel, you'd pay $9 for the same bottle.

Worse, once you order a bottle, it's rare that you'll be asked if you want another. Your server will simply open another to top off your glass -- and your tab.

Today's Tip: If you want tap water, ask for it specifically.