Pulse Electric Field Devices (PEFDs) have been used as the sole source of water treatment in evaporative cooling water systems for over 10 years often with good results. Several field evaluations will be presented that provide detailed data on microbiological control entirely by the PEFDs. This paper will present both field and laboratory test data independently obtained from operating cooling tower water systems that rely solely on PEFDs for microbiological control. This data shows that adequate and acceptable control of both planktonic (bulk water) and sessile (biofilm) microbial populations in numerous full-sized cooling tower systems in being obtained. A comparison of field versus lab microbiological testing methods and results will be presented that indicate if proper Guidelines will be provided for field microbiological monitoring.