Water isn't just wet. It can also be hard or soft. In fact, water can be soft, hard, moderately hard, very hard and even permanently hard. These are all specific designations, among those paid to think about such things, with measurable differences. Sapna Parikh has the story in today's DNews dispatch.
Water hardness has to do with mineral concentrations. When water passes through rocks and soil, or is stored in wells, it picks up soluble minerals like calcium and magnesium. The higher the concentration of these minerals, the harder the water. The United States Geological Survey classifies hard water as anything with more than 6o mg of calcium carbonate per liter. Check out Sapna's report for more details on hard water and its relationship to delightful substances like soap scum, limescale and magnesium stearate.
Chicago Tribune: Hard facts about tap water
BBC: Hardness of Water
Popular Mechanics: The Expedited Explainer: Hard vs. Soft Water