Discolored water can be associated with a variety of different plumbing problems. Iron and magnesium buildups lead to black water. Although these minerals are not dangerous, homeowners can contact a company that specializes in water softening like ServiceMark Heating, Cooling and Plumbing to discuss how to filter these minerals out of their water. The water softener that is used in a home can also cause a discoloration if resin beads get into the water.