The first step in repairing a leaking garbage disposal is to find out the exact location of the leak. There are four places that the garbage disposal unit may be leaking from. It is important to determine if in fact the garbage disposal is leaking from the unit itself or rather if one of these other pipe intersection points is causing the leakage.
It the water is leaking where the garbage disposal connects with the sink and the leak is running down the disposal unit, then the connection between the sink drain and the disposal unit must be resealed. This can be done using standard plumber's putty found at a local hardware store. Unplug the disposal unit and loosen the connector ring located around the top of the unit just below the drain. Once this ring has been loosened, pull the disposal unit down to remove it from below the sink. The metal ring that sits in the drain on top of the sink tub can now be removed. Apply the plumber's putty to bottom of the ring and put it back into place to repair the seal. Reattach the disposal unit and check for leakage.
If there is still water leaking, make sure that the points where the dishwasher and the unit's drainpipe connect are sealed tightly. Finally, if water is leaking from the base of the unit itself, and all other seals have been checked, then the unit needs to be professionally repaired.