It rains about three months a year in this Mexican state, and then nothing. If there's not enough rain, women like this woman have a lot of work. That woman lives in this poor mountain village, population about 400. She says, �until a few years ago when it was dry, she and the others here had to get water from a canyon, a day's walk there and back.� then three years ago, the villagers attached a plastic pipe alongside the sloping, metal corrugated roof of the local craftshop. The pipe dumps rainwater into a small covered tank. Now the woman says not only do they have more water, they have better water. She says, �before the pipe system was invented, the villagers collected rainwater from a palm in a field. Animals drank there and pigs bathed. Everybody here used to get sick.� Putting a pipe alongside a roof might not seem all that ingenious or revolutionary because it's not. �There were harvesting system that were very old, we could say about 5,000 years,� this man coordinates the International Center for Demonstration and Training of Rainwater Harvesting System. The school is in a town just outside of Mexico City. On campus they're testing various types of rainwater catchments systems. He says, �This is a system we have for a four or five member family.� The bigger the roof, of course the more rainwater that can be collected. We walk a little bit further and the man points to a modest sized office building and next to it a huge hole in the ground that looks like an Olympic sized swimming pool with a cover on top. He says, �it looks like a huge bath. This means this avoid contamination, avoids solar radiation, and that keeps the rainwater in good quality.� That bag contains enough water to sustain 2,500 people for a year. The stored water runs through a basic purification system. The investment per person? About $35 dollars. Still only a handful of communities in Mexico or elsewhere are doing this. That's because in many places people have been taught that rainwater isn't clean and in polluted urban areas it isn't. but necessity is the mother of invention. �The drought in Australia has been ongoing for about a decade in most locations,� this professor studies Rainwater Harvesting at the University of Newcastle in Australia, the planet's driest inhabited continent. He says, �We've got this bizarre situation in Australia where we're in a water crisis but none of the water running off of extra areas is actually used to solve that crisis.� That's changing in parts of Australia. In the city of Brisbane one in eight residents now have water tanks and collection systems. It used to be illegal, now it's mandated for new buildings. This man says this has saved Brisbane tens of millions of dollars. He's the author of the book �Rainwater Harvesting for Dry Lands and Beyond.� He says, �before going forward with this water harvesting, they were looking at putting in multi-million dollar desalinization projects, large dams and large canal projects. But if they get every home hooked up with one of these rainwater tanks, they won't need to do any of that for 100 years. And that's at projected population growth.� And he says the benefits of rainwater harvesting don't stop there, �In addition it can be used to reduce flooding downstream because instead of that water flashing off the roof and into the storm drains, we're collecting it and holding it and then distributing it over time.� Rainwater collection isn't ideal everyplace. It's difficult to do in densely packed urban areas, there's more pollution and less space for collection. And you need the right roof. For example, if you're living in a place like the United Kingdom, old copper roofs can leech metals into rainwater. And parts of the US, roofs are coated with asphalt shingles that can add toxins. Still any economist will tell you, when faced with a chronic water shortage changing a roof is a lot cheaper than any other existing alternative.