Squirt a small amount of white toothpaste on the water mark. A pea-sized amount is adequate for most of these spots.
Rub the toothpaste into the mark on the table by using a soft, damp cleaning cloth. Use a circular motion to do this.
Check the water mark after a couple of minutes to see if it is gone. If not, add more toothpaste if necessary, and continue rubbing.
Wipe away the toothpaste residue with a clean section of the damp cloth.
Mix a solution with the ammonia and 1/4 cup of water in a medium bowl.
Wet a cleaning cloth in the solution, and wring it out.
Clean the water mark with the damp cleaning cloth by using a circular motion. Do this lightly to prevent removing the finish.
Look at the water mark after a couple of minutes to see if it is gone. If not, continue cleaning it.
Rinse the table with a damp cleaning cloth once the water mark disappears.