Take it apart and clean the O-ring and both the base with the O-ring grove and the lid of the water valve, then when you put it together tap on the clamp on the opposite sides of the clamp from the nut you are tightening to make it draw up properly, while tightening the nut. If the valve still leaks call 800-621-5886 for customer support.
NEVER STAND OVER ANY POOL EQUIPMENT WHEN TURNING ON THE PUMP!