A watery puck of coffee grounds after pulling a shot of Espresso is an indication of uneven extraction of coffee grounds. It's not a very serious alerting problem as long as you are satisfied with the taste of Espresso you get. If you want to get rid of the watery puck, you must be very careful about these two things. The size of the coffee grounds must be even and consistent, and you must tamp the coffee properly in the portafilter.