This idea isn’t completely new. Balancing inflow with outflow — or mass balance — is a routine part of planning large-scale water projects like building a dam or delivering drinking water to a city. Applying that concept to local groundwater is also not without precedent. Tushaar Shah, a senior fellow at the International Water Management Institute, a non-profit devoted to researching sustainable use of water in developing countries, traces the idea to American experiments in the 1980s and 1990s, especially in Kansas where local institutions brought groundwater users together to manage demand through water permits. Mexico has also tried community management of local aquifers. And in India, more than a decade ago, the Food and Agriculture Organization of the United Nations funded a project in the state of Andhra Pradesh to introduce water monitoring and budgeting.