Water conservation has become a critical issue in recentyears. Evaporation in cooling towers can be asignificant source of water consumption in commercialbuildings; however, most cooling tower models used inwhole building simulation programs are eitherprohibitively time-consuming or overly simplistic withrespect to water consumption. Therefore, it is difficultto determine the effects of control strategies on waterconsumption using these models. This paper presents anew polynomial based model which defines the waterloss by evaporation as a function of tower inletconditions. The polynomial coefficients have beenderived through a multi-variable regression performedon data generated by a detailed finite difference model.Test cases show improved agreement with the detailedfinite difference model compared to several otherexisting models. In addition, the execution time of thenew model has been found to be much faster than thedetailed model and comparable to those of othersimplified models