1.) The water level in the toilet tank is too high.
2.) The chain in the toilet tank is too short, too long or is corroded and kinking up.
3.) The rubber flapper is worn out and needs to be replaced.
Lowering the water level. Locate the hollow tube inside the tank. Is water running over the top of it? If yes, we need to lower the water level within the tank. The main apparatus of the toilet has a float on it which rises up and down with the level of water in the tank. There is a rod (plastic or metal) that runs alongside the float. Turn this rod with a standard screwdriver to lower the float. The float, when raised by the water, turns off the water. You want the water level to be within 1 inch from the top of the hollow tube.
Adjusting the chain. There is a chain which joins the flushing handle to the rubber flapper located inside the water tank at the bottom. If the chain is too long it can get caught under the flapper, keeping it from closing which allows the water to continue to flow. If the chain is too short, again it will keep the flapper from closing. Use a long nose or needle nose pliers to lengthen or shorten the chain. Allow about 1/2 inch of wiggle play left and right in the chain. This will allow enough slack for the flapper to operate correctly. Sometimes this chain becomes corroded, in which case it needs to be replaced. Use the long nose pliers to remove the chain and replace with a new one.
The rubber flapper. If the water is still running, inspect the flapper for deformations or cracks. If this is the case, it needs to be replaced. Using your long nose pliers to remove the flapper, take it to the hardware store and purchase one exactly like it, install it, hook up the chain according to the above specs.
Benefits: Some simple adjustments will save water and money on your monthly expenses.
Cost: These easy to do it yourself adjustments cost little to nothing.
Tools needed: A screw driver and a long nose/needle nose pliers.