A running toilet is annoying and wastes a significant amount of water. Two good reasons to attend to it promptly. Usually, adjustments are needed to the float arm, which stops the water from entering when the tank is full. It could also be that the tank ball guide wires are broken or entangled, keeping the ball from resting tightly on the valve seat. Tank balls, as well as the valve seat, can deteriorate after time and will need to be replaced. Doing this is not a complicated job and all of the replacement parts can be purchased at hardware or plumbing stores. If none of this works or you simply don't know what to do, contact a plumbing professional.
