Nowadays the theme of rainwater collection is achieving more and more importance. It is indeed a very good way to reduce water consumption or to compensate water lack. The choice to have one rainwater collection system for each house or building is probably the best choice to count on for the short period because allows each individual to start doing some active adaptation with respect to water needs. In this sense there are quite many already existing and accessible systems and solutions; it is sufficient to search "rainwater collection" to find plenty of interesting links, e.g. (unarranged list):
Of course, before doing more, one can simply start now trying not to waste water. But I think in the world active adaptation on rainwater has already started. And, to find the best systems not to waste water and rainwater is our challenge, whatever it takes to get there...