https://en.wikipedia.org/wiki/Super_hydrophilicity
https://en.wikipedia.org/wiki/Superhydrophobicity
It could just collect water into it, and using natural gravity it would accumulate @ the bottom where you could then, simply collect/filter it, and use it to run a HHO generator which who essentially fill the aircraft/dirigible, and power it, simultaneously...
Collecting water from the air itself...
https://en.wikipedia.org/wiki/Troposphere
Program the damn thing to track weather patterns, along with the usual air-pressure & humidity patterns.
You could essentially, fly through clouds to absorb the water, or just keep flying within specific patterns along with the humidity patterns of the EARTH.
If you wanted to do it the cheap hacker-way, and small scale...
https://www.youtube.com/watch?v=BY7uGJGvo9w&feature=rela...
http://hackaday.com/2007/12/27/24c3-build-your-own-uav/
https://en.wikipedia.org/wiki/Rain-X
A small jar HHO generator which would then feed a micro-engine(like in a R/C car) powering an electrical generator which would feed power to the HHO generator. This is already being done commercially.
Solar is a way better way then combustion in the end but, its the closest thing to a TYPE-2 civilization WE will see...
;-)