Of all the space-saving bathroom designs I have seen this one, the Vertebrae, is the clear winner. It is an ingenious stacking design that incorporates all of the necessities of a bathroom in to one tiny 4 square meter footprint.
The Vertebrae is a stack of swiveling units. Each unit contains a piece of the bathroom. The upper most sections are showerheads, followed by storage areas, a sink and finally a toilet on the bottom. There are even compartments on the sides of the toilet for toilet paper and a toilet brush.
The unit is entirely self-contained with a drain on the floor and you have yourself a compact bathroom. Each unit is made of aluminum and completely customizable.
The two major drawbacks are the appearance, which is perfectly suited for an episode of Star Trek, but may be a bit ultra modern for less a cosmic decor. The other drawback is the price. At $20,000 it may well be beyond the reach of some consumers, however $20,000 is perfectly reasonable in some markets.