First, there is not actually any mud in the water delivered to your home and no mud can enter our pressurized water lines. However, there are minerals in the water that can settle in the main lines or accumulate on older household plumbing made from galvanized steel pipe. The two minerals that can cause the water to be discolored are iron and manganese. Neither of these minerals are harmful. They are found in most vitamin supplements. These minerals can accumulate in the bottom of the main lines over a number of years. When pressure changes occur in the water lines from line breaks, flushing of hydrants, fire use of hydrants, filling swimming pools or rapid turning on of the water (bathtub filling), these minerals can re-dissolve in the water and make it appear muddy.