I do not advocate mixing water fowl with other fowl. I like all of my livestock in their own runs and coops. Ducks and geese like water and are very messy. Ducks are messier than geese I am told. I raised ducks last summer and I have never seen such messy mucky things. These animals are better served living amongst their own kind in their own environments in my opinion. There are people that do mix them but I do not.
If you have the room, it shouldn't be a problem. We free-range domestic geese, ducks and chickens, with no issues. As mentioned, waterfowl can be messy, but still a joy to work with if you have the time and space.
Be careful with some of the aggressive species such as the Egyptian Geese, even hand-reared birds can become quite nasty towards other birds.
Water fowl and chickens will fight some, same as all birds, to set a pecking order. The only thing you really have to worry about if you have ducks and geese together is making sure that everyone has a mate. If you have extra ganders and ducks with them they will try to mount the hen ducks. My geese and turkeys free range kind of in a very large fenced in area, probably a half acre. The toms and ganders will chase each other some times and then forget all about it. This year we are going to set up separate pens. Jenn
It depends on numbers. If you have only a few waterfowl, it may not be practical to have separate housing. It also depends how clean and how much room they have. Waterfowl require lots of water, and for this reason I keep them separate with a tank w/float valve. Otherwise, I'd spend my entire day bringing water to the ducks and geese.
Oh, and I'm only replying because my wife is from Teesside. Durham is one of my favorite City's anywhere in the world. I love it up north.