The inventive method and apparatus for treating water and water systems. The apparatus and method also assures the retention of calcium in drinking water provided to an animal by suppling water to a water feed line which is connected to a drinking device, oxidizing the water to retain calcium in the water in solution, ionizing the water using copper/zinc electrodes, the ionization sanitizing the water and providing residual copper and zinc ions which act as an algicide and a biocide, and providing the ionized oxidized drinking water which retains calcium in solution to the animal for drinking.