Simple Green: Water Jug In The Toilet Tank

This trick is an oldie but goodie, especially if you have an older toilet that's not low-flow. Fill a large plastic gallon container with sand and water and place it inside the toilet tank. This will save you roughly three liters of water every time you flush. However be warned: don't do this if you already have a low flow toilet. Without the right amount of force, toilet contents will block drains going out to the sewer.