To get rid of chalky calcium deposits left by hard water on your porcelain sink, tub, or toilet bowl, try rubbing
the stain gently with a pumice stone. Or cover it with paper towels and soak with vinegar. (Empty the toilet bowl first by turning off the water-supply valve and flushing twice.)
After an hour, remove the towels, rinse, and scrub with cream of tartar on a damp cloth. For darker stains, use household bleach instead of vinegar.
Minerals settle more quickly out of hot water than cold, so they collect on the bottom of your water heater, reducing its efficiency; they may also narrow your hot water pipes. To protect the water heater, have a plumber delime it annually. The only remedy for clogged pipes is to replace them.