If you have an older, conventional toilet, you are probably using more water than you need to, to clear the bowl. You ought to consider installing a new, low flush toilet, but until you do this, the Toilet Tank Bank displacement bag will reduce the amount of water in your existing tank by about 0.8 gallons, saving that amount of water with each flush. Over time this can add up.
Fill the displacement bag with water, close the valve to prevent eventual evaporation, and hang the bag inside of the tank of the toilet with the bag’s hook. Saving water has never been easier.