When I am cooking this from its frozen state, I don't add any liquid to the bottom of the crock pot because as the roast thaws it will release plenty of liquid. If the meat is fresh or thawed, I add 1/4 to 1/2 cup of water or chicken broth. Likewise, if you get a pork roast that has not had broth and salt added to it, you may want to add more salt.