Place a cloth over the stain. An iron set to medium and iron the cloth.
A dab of toothpaste on a damp cloth and gently rub in a circular motion.
If it's wood furniture, you can try rubbing a little mayonnaise into the water stains.
To remove white rings left by wet glasses on wood furniture, mix equal parts vinegar and olive oil and apply it with a soft cloth while moving with the wood grain. Use another clean, soft cloth to shine it up. To get white water rings off leather furniture, dab them with a sponge soaked in full-strength white vinegar.
Silver polish also does the trick.