DO NOT put it in a jar with water! To make hash oil you have to flash freeze the bud/trim with butane. And the other dude's right, it takes a lot to make a little, so if you don't have very much to work with it won't be worth it.
The water thing is how to make bubble hash, but the water needs to be as cold as possible before you add the skuff. Water can get down to like -2 degrees celsius before it actually freezes.