What would cause my ford 2001 sport trac to use 1 gal of water every 15 miles. No leaks, new hoses and new radiator, new thermostat and no water in oil or tranny fluids. 115k miles.???

You dont use water, for Ford you have to use Conventional 50/50 COOLANT! water steams right off. Pressure test head gaskets, just in case. A simple tool you can rent from Auto zone, screw the gauge into each spark plug slot and pull the fuel pump fuse and turn the engine each time for the same amount of time on each cylinder to get an accurate reading. OR rent a different head gasket tester, a combustion gas detector, you put that in the radiator cap and run the engine and itll test for combustion gas in the radiator system.