Dab a small amount of toothpaste -- not gel -- on a clean, damp cloth. Rub the toothpaste into the water mark in a circular motion until the water mark is gone. Wipe the toothpaste from your table with an unused portion of the cloth. Allow the treatment to dry completely, and repeat if needed.
Cover the water mark with a thick cotton cloth. Press a dry iron, set at medium heat, on the cloth for a few seconds. Lift up the cloth and check the water mark. Repeat as needed, pressing only a few seconds at a time.
Mix equal amounts of cooking oil and salt to make a paste. Rub the paste onto the water mark with a clean cloth. Wipe the table clean with a slightly damp cloth when the water mark is gone.
Combine a spoonful of cooking oil with a spoonful of ash for a paste. Rub the paste into the water mark, and wipe it off with a clean cloth.