First off, if you are worried about the quality of your water, you can buy home testing kits in any hardware store. Secondly, silver is rarely pure. If it contains trace minerals, it can appear bluish green. I have very acidic water, and I have copper and brass pipes. This turns my sinks and bathtubs blue. I am not sure if it could hurt older silver, but it might. Test your water first to ensure your water is drinkable, then call a jeweler to ask about the discoloration of your sterling silver.
