Calcium and magnesium salts are the minerals in water which are responsible for its hardness. The Findlay Water Treatment plant has an average hardness of 140 milligrams per liter or 8 grains per gallon. Hardness does not affect the safety of water. These minerals may accumulate in coffee pots. To remove them, fill the coffee pot with vinegar and let it sit overnight. Then rinse the coffee pot thoroughly before using. Vinegar will also work as a soak for clogged shower heads and faucet aerators.