Winding rods, built into the stator of an electrical machine, are no longer safe to operate after leakages in a water chamber. After this waterchamber has been removed, as is necessary anyway, a flexible, gas-proof hose is pulled upon the rod end, and the machine-side end of the hose is attached to the rod in a gas-proof manner. The other hose end is connected to a vacuum pump and, by evacuating the hose, the water that has penetrated into the rod insulation is removed by the same route as it penetrated into the insulation. The quality of this drying process is monitored by dielectric measurements.