The volume of water in the tank, its height above the bowl, restrictions or blockages between the tank and the bowl, or within the bowl all limit the speed and amount of work the tank water can perform. If your toilet is less than ten years old, you may have a first generation 1.6 gallon low flush toilet. These toilets were mandated by the 1992 Energy Policy Act in an effort to save water. Traditional toilets used 3.5 gallons of water per flush.