Combination UV and micro filter water purification system.  The problem with UV systems is, of course, the electrical requirements.  My current filtration system is a gravity feed, so no power is required, but any combination with UV would require an external power source..  A pump action filtration system could also double as the generator for the UV circuit.  By mechanically pumping the system you can pump the water, and generate the electricity needed for the UV lamp.  -- Is there a way to generalize this contraption for generic functionality?  A combination hydraulic pump and electric generator?  Small too.

I knew I shouldn't have bought that hybrid vehicle it's got me thinking weird synergistic thoughts.