The present invention is directed to a method and apparatus for preventing damage to drapes and to heating and cooling mechanisms used in conjunction with apparatus for containing and thermally treating sterile liquid, and to preserving the sterile field when using such apparatus. A surgical drape is combined with a sensor, preferably attached to the drape, to detect whether or not liquid is present in a drape container conforming to a heating/cooling basin. An alternative embodiment employs sensors at opposite surfaces of the drape to measure conductance and, thereby, leakage through the drape. A microprocessor in each embodiment receives a signal representing, for example, an electrical conductance measurement from the sensors and determines if liquid is present, or alternatively if the conductance is sufficient to represent the presence of a leak. If liquid is not present or a leak is determined to exist, the microprocessor disables a temperature controller for the basin to prevent damage to the drape and heating and cooling mechanisms.