S. Vishwanath provides us with two short clips from a recent trip to the Northeastern states: This one shows ad-hoc or 'opportunistic' rooftop RainWater Harvesting in Manipur -- improving these systems and propagating them will help alleviate people's water problems.
And this one shows a primitive toilet from the same state. Vishwanath sees this as a strong opportunity to implement 'eco-san' What's 'eco-san' ? Here's a lot of resources about eco-san, and here's a short movie showing an inexpensive bamboo ecosan toilet (can be built for Rs 4000/- in 2 days, and has a bathspace included).