George Foreman
Very little, if any, water vapour results from the burning of gas turbine fuel. The con trails are ice crystals that form around the 'smoke' particles/nucleii in the gas turbine exhaust plumes. The ice crystals form only in near to 100% water vapour saturation in the atmosphere and best when the air is a little over the 100% saturation - called super-saturated but needing a condensation nucleus to trigger the change of state from vapour to ice crystal.