Simple Pot Roast in a crock pot, no soup or gravy?

I am looking to make the pot roast my mom used to make in a crock pot: meat, carrots, potatoes and onions (and a small amount of water as needed--only! no gravy, tomatoes in juice or soup), but I am not sure on what temp or for how long, or with how much water, I should let it cook. I know she always let it slow cook, but I'm open to your suggestions. Thanks!