People were lining up with buckets to get water from a truck last year in Monterrey, Mexico, as two of the city’s three dams almost completely dried up. Now Tesla has plans to build a huge electric car “gigafactory” in that same water-insecure city. A gigafactory is Tesla’s term for its massive assembly and parts plants. The Monterrey one will be built on 4,200 acres — twice the size of the…