MIDLAND – On a recent morning, Tommy Taylor, a manager with the drilling company Fasken Oil & Ranch, stood in the West Texas desert beside two huge pools of water. One contained freshwater, and the other contained brackish water from the Santa Rosa aquifer 1,700 feet beneath Taylor’s feet. Fasken has been mixing the two sources as part of a pilot program to use brackish water in hydraulic fracturing, so that the water-intensive drilling process doesn’t deplete local freshwater wells.