The water level in your toilet bowl is affected by several factors. The main contributing factor to the bowl's water level is the tank fill level. If the tank level is low, the toilet flushes inconsistently and does not fill properly. When this happens you must adjust the fill valve to allow more water into the toilet bowl. Adjusting the fill valve depends on which type of valve you have in the toilet.
Lift off the toilet tank lid and set it to the side on a flat surface. Inspect the fill tube to ensure the end of the tube is over he mouth of the overflow tube.
Position the fill tube directly over the overflow tube, if it has come away from the overflow tube. The fill tube directs water into the bowl and connects from the fill valve onto the overflow tube with a clip. If it is not over the overflow tube, the toilet bowl does not fill with water properly.
Find the screw on the top of the fill valve where the float ball arm connects to the valve. Turn the screw clockwise with a flat-head screwdriver one full turn. This raises the float ball, allowing more water into the tank. Flush the toilet and allow the tank to fill and check the water level. Continue adjusting as necessary.
Pinch the retaining clip on the side of the float if your fill valve uses a float directly on the valve. Lower the float slightly and release the clip. Flush the toilet and check the water level. Place the lid back over the tank once adjustments are complete.