Outside my area of expertise! But in case this is at all helpful: I think the basic apparatus is pretty much standardized. However, tasks of varying complexity can be designed using the same tank. There has been an awful lot of research using the Morris water maze paradigm over the last 40 years, and it would be worth your while to search PsycINFO - maybe also contact recent authors directly.
One last thought: If you became the first to devise a series of progressively more challenging water mazes, you would make a name for yourself. Could be a long-term research program.