Immigration and border security will be the likely focus of U.S.-Mexico relations under the new Trump administration. But there also is a growing water crisis along the U.S.–Mexico border that affects tens of millions of people on both sides, and it can only be managed if the two governments work together. Climate change is shrinking surface and groundwater supplies in the southwestern U.S. … Growing water use is already overtaxing limited supplies from nearly all of the region’s cross-border rivers, streams and aquifers. Many of these sources are contaminated with agricultural pollutants, untreated waste and other substances, further reducing the usability of available water.