Addendum: After much deliberation and soul searching, we decided to use the funds for the rainwater harvesting tanks to build an office for the teachers. In the long run, an office will give teachers an incentive to stay in Tongo (which has been a problem in the past), and it will provide a lockable place to store classroom materials like books and maps. And sadly the probable fate of the cisterns is that they would not be properly maintained and end up being unused in a matter of years (like everything else in Mali).
Building the cisterns is still a possibility, depending on what funds we have left over, but they're on hold for the moment.