if your toilet was built prior to 1990, you could cut your personal water consumption in half by replacing this one feature.  visit http://www.toiletabcs.com/toilet-water-conservation.html to learn more and http://www.libertyplumbing.org/ to get a new toilet installed.  Location of the water rating stamp noted with arrow.  If you cannot find this stamp, your toilet is costing you money.  It is going down the drain!