In recent years, reuse of municipal waste water as the coolant in drift-producing cooling towers at electrical generating plants has become increasingly common. A hueristic model is presented that can be used to estimate the concentrations of viable airborne microbes in the drift from a wet cooling tower given the concentrations of microbes in the cooling tower. The purpose of this presentation is to allow the nonmeteorologist to understand the factors affecting airborne concentration and to make crude estimates of ground-level concentrations of airborne microorganisms. Concentrations are calculated using a standard meterological method, the Gaussian dispersion model, in which terms have been included for droplet settling and microbial death rate.