Answer to Question 1
Hard water has high concentrations of ions, mostly calcium and magnesium. Hard water reduces the effectiveness of detergents and causes mineral buildup in pipes and appliances. Soft water has low concentrations of dissolved ions. Soft water is reactive and could dissolve your pipes, leading to unhealthy levels of metals in your water.
Answer to Question 2
Ground water that flows through hot rocks heats quickly, and since water has a high heat capacity, it retains much of the heat energy as it moves toward the surface to discharge as a hot spring. The heat source can be an adjacent shallow magma chamber (e.g., Yellowstone) or deeply circulating ground water that flows upwards along a contact between sedimentary rock and less permeable crystalline rock (Warm Springs, GA).