Why does the water rust my plumbing fittings and water heater?
Any water will cause corrosion of metal. Cayman Water supplied desalinated water is relatively more aggressive than naturally occurring fresh water due to its low total alkalinity, its softness (lack of mineral content) and the residual salt present. Unlike many places in the world where hard water and scaling are problems, piped water in Grand Cayman is the opposite. It is very soft water thus more corrosive. Use plastic, brass or other corrosion resistant materials in your plumbing, especially for hot water heater fittings. Do not use galvanized steel fittings in your hot water plumbing to ensure prevention of leaks. Also, keep your hot water heater temperature as low in your comfort range as you can, which will mitigate corrosion and prolong the life of your water heater element.