Remove the lid from the bucket of joint compound and use the putty knife to take a few scoops of compound out of the bucket. Put the removed joint compound in the mud pan and set aside.
Fill the void in the joint compound with water.
Attach the paddle mixer to the electric drill and plug in the drill.
Insert the paddle mixer into the bucket of joint compound and stand over the compound, with your feet pressed firmly against the sides of the bucket to prevent the bucket from spinning around when you turn on the drill.
Turn on the drill and work the paddle mixer around the joint compound until the water and compound is thoroughly mixed.
Check the consistency of the joint compound, which should be runny like thick paint. If the compound is too thin, add some of the compound you set aside in the mud pan and mix it again. If it is too thick, add some more water and mix.