Each flush only uses 1.6 gallons of water. The National Energy Policy Act of 1992 stated effective January 1, 1994 that all water closets shall be 1.6 gallons per flush maximum.
Before you begin the steps to determine what caused the problem, it is essential that the bowl is clean. This may mean that you have to flush a few times or, if your toilet is completely clogged, you may need to plunge.
Important: Do not continue to the next step until the bowl is clean. If you're having trouble getting the bowl clean, you may need to consult a plumber.
Open the supply valve all the way.
Remove the lid from the tank.
Make sure the refill tube is connected from the water control and inserted into the overflow tube without being kinked or damaged.
Adjust the water level. It should be no lower than 1/2" below the top of the overflow tube. If it is lower than 1/2", raise the water level by turning the top screw on the water control counterclockwise. (You may need to flush after adjusting the screw to get the water level to rise.)
Measure 3 arms lengths of toilet paper and put it in the water in the bowl.