An evaporative cooler, including one or more media modules, distributes water from a source of water to each module through a constant flow valve. A distribution unit at each media module includes a spray bar for spraying water through a plurality of uniformly spaced holes having an aggregate area equivalent to or less than twenty five percent (25%) of the internal cross sectional area of the spray bar. A distribution cap distributes the streams of water to the underlying media module(s) and the water dripping from the media module(s) is drained. A fan or other air moving device draws air through the media module(s) to obtain cooled air resulting from evaporation of water flowing downwardly along the media module(s). A microprocessor controller, responsive to any of one or more sensors for sensing the temperature of the air flowing into and out of the media module(s), the relative humidity of the air flowing into and out of the media module(s), the pressure differential between the upstream and downstream sides of the media module(s), the temperature of the water flowing to the spray bar(s), the fan speed, and the pressure differential between the downstream side of the media module(s) and the downstream side of the fan, controls the flow of water and the fan speed.