Standards for overhead emergency safety showers used for decontamination in laboratories and production sites specify the spray pattern and the water flow rate. Up to now, there has not been a scientific basis for these requirements. The decontamination of water-soluble contaminants has been investigated using 15 customary shower heads at 20 to 110 L min(-1) water flow rate. A general relationship between water flow rate and decontamination effectiveness could not be established: At a flow rate of 30 L min(-1) the wash-off time in general did not exceed the time observed at considerably higher flow rates. The shortest decontamination time has been found with a spray pattern that does not fulfill current standards.