Hard water has a high mineral content, most often magnesium and calcium. These elements can be picked up by groundwater as it passes in and around soil and rocks. Water hardness is measured in grains per gallon (GPG), parts per million (ppm) or milligrams per liter (mg/L). The Water Quality Association considers water to be hard if it has more than 17.1 ppm or 1 GPG. According to a U.S. Geological Survey, 85% of the water in the United States is considered hard water.
If your home has hard water, you’ll notice mineral deposits, stains or a white film on surfaces like porcelain, enamel, china, stainless steel, tile, chrome, fiberglass, and glass. You may notice stains or build-up on bathroom fixtures, dishes, and sinks. In addition to magnesium and calcium, manganese, brass, iron or copper can also be present in the water. Manganese stains look brownish or black, while iron-rich water leaves deposits that look red or like white slime. If you notice blue or green stains around your plumbing fixtures, your water may be slightly acidic, which can erode brass or copper pipes.