Designing a Water Purification System for Developing Communities

For my senior project for my BS. in mechanical engineering , I'm thinking of designing a water purification system, perhaps powered by solar energy. The senior is a one semester course for a team of two Mechanical engineers. I know that one way of doing this is passing the water through sand/charcoal/gravel and than through UV treatment . However ,I'm not sure how much of the mechanical engineering principles I have take could be applied to this project. Does this make a good one semester project .Also there is no sponsoring so how high could the budget get if I want to make a prototype.