You don't say what size cage your bird is in. My Rosetta was pooping in her bowl a lot until I realised she was able to swing over the bowl and poop at the same time. I rearranged the cage and things are a bit better. She still poops in her water if she's climbing the cage wires directly above it.
The thing is 'setta's cage is far too small for an active corella. She needs a lot more floor area to be able to run and play. She also needs space to fly from ground to perch in order to get a reasonable amount of exercise during times when she's in her cage (which is most of the time for the moment).
My best advice is to put most of the fun things in your bird's cage on the opposite side to his food and water. I find that placing perches across the diagonal works well (gives the bird max distance to fly or hop-fly between perches), but if you do that, there's always the possibility of pooping in water.
For a Ringneck, I'd say the very smallest cage footbrint would be something like a metre by sixty centimetres (3 foot by 2 foot). Bigger would be better, though.
Oh and PS. The other thing you could consider is to place a platform up level with the bird's main perch and place his water on that. Or, purchase a large, cage-wall-hanging water container big enough for birdie to bathe in.