Abstract: A method and apparatus for automatically maintaining gas turbine NO.sub.x emissions at a substantially constant level during all ambient conditions and for no load to full load fuel flows. The required water/fuel ratio is calculated for a substantially constant level of NO.sub.x emissions at the given operating conditions and, knowing the actual fuel flow to the gas turbine, a signal is generated representing the water metering valve position necessary to inject the proper water flow into the combustor to achieve the desired water/fuel ratio.