Do slow cookers require liquid to operate? I have a Butterball turkey breast roast that I'd like to cook tomorrow, and I'm planning to do it in my slow cooker.

The recipe as provided online is the same one that is on the turkey packaging:


  Slow-Cooker Instructions:
  Place THAWED roast, skin side up, flat in 8” diameter slow-cooker. Add 1/2 cup water. Cover, cook on low 7-1/2 hours to internal temperature of 170 degrees as measured with a meat thermometer. After 4 hours, check temperature at center, ends and near top for food safety. Turkey must reach 140 degrees within 4 hours. 


Now, I haven't done a lot of slow cooking before, but when I have, I've always added enough liquid to fill the slow cooker up to about 3/4 full.  Half a cup of water will barely cover the bottom of my slow cooker.

I did some research, but found nothing conclusive.  Some people say that slow cookers should always be more than half full, while others seem to indicate that it's fine to run them almost empty.

Is there a minimum level of liquid necessary when cooking in a slow cooker?
It's really no different from cooking something on a stove: if you have no liquid at all, things are probably going to start getting too hot, sticking on the bottom, and maybe burning. As long as there's some liquid, you'll be fine. The important thing is to add enough; if you keep having to open it to add more, it won't stay hot. This is basically the minimum level: enough that it won't boil dry in an hour or so. If you're cooking something really simple like a piece of meat, using too much water just provides more water for the flavor to get diluted into.

This is precisely what the first page you linked to says: if it's not full enough, it might all boil off. The writer is just way off about quantities. I suspect his cooker's lid doesn't fit well, or he's unnecessarily cooking on high. I don't think my slow cooker would boil dry from half full in 8 hours on low, and there's no reason to put it on high if I'm cooking that long.

The recipe at the second link isn't exactly empty - a can of cranberry sauce will provide a good amount of liquid. It also might not be a great recipe. On that note, I might suggest you look for more authoritative recipes. Perhaps check out a slow cooker cookbook from your library (these tend to be pretty common) to get an idea of the kinds of things you can do. (Of course, if all you want is a plain piece of meat, I guess you don't need much.)