(A note about wading pools - make sure that water circulates, either via a flow in/off the map or screwpumps. Some contaminants can be spread after they are (partially) washed off.)
I'm currently installing a hospital w/ an automated mister at the entrance, so 100% of patients get the cleaning treatment (and a happy thought to balance out the loss of that spleen).
Requires (at least) a 2-tile long entry way - 1st tile is a pressure plate, 2nd tile is the delivery point of a stack mister:
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http://dwarffortresswiki.org/index.php/DF2014:Mist#Stack_generatorPumps are permanently powered. Pressure plate is linked to a hatch that sits over the output of the lower pump (the pump that "sucks in" the water" that just hit the floor below the mist). That water sits there in a 1-tile big, 3/7 pool indefinitely, until someone walks in - then the hatch opens immediately, and the water starts cycling, instantly creating the welcoming mist before the dwarf can take that next step into it. 100 ticks later, the hatch closes, the upper pump has nothing to suck up, and the water is deposited in that lower tile again, minimizing any FPS issues.
This has the added benefit of a mist display for anyone who is in a nearby bed, and the medical staff.
If you want (I did) you can go with a 3-tile long entry and install a 2nd pressure plate to clean all who leave.
(Misters are pretty easy to set up w/ a water reactor powering it from a couple levels below. I use a similar mister (but double-wide) at the grand entry to my dining room/tavern. I figure 99% of the dwarves will go there sooner or later.)
I also put a dedicated well near the middle of the hospital for the old-fashioned cleaning option. Takes some work, all told, but it's the right move. Designated as a water source but not a meeting place (don't want a crowd there interfering with your medical staff, and I'd rather they all socialize at the dining hall.)
@ all: afterthought - related Question:
I like to use 3-d designs whenever possible, using "up/down" as shorter access to stores/rooms/whatever, rather than walking miles across a single z-level. Is that possible w/ a hospital, to designate 3 zones on top of each other, connected w/ ramps/stairs? If I treat a patient in one zone will they find the hospital beds in the rooms in the next zone down?
I'm guessing that "stores" from a "storage hospital zone" will not be stolen by the "surgery hospital zone" above it, correct? But if I put traction benches and bedrooms in a vertically adjacent zone, will those work?