A thermo-hydraulic performance optimization analysis is presented, yielding simple algebraic formula for estimating the optimum performance point of counter current mechanical draft wet cooling towers. The effectiveness-NTU method is used in the present study, together with the derivation of psychrometric properties of moist air based on a numerical approximation method, for thermal performance analysis of wet cooling towers of the counter flow type. (C) 2003 Elsevier Ltd. All rights reserved.