Unless the circulation water is drained, it may freeze in winter and cause the pipes to crack.  If the drain of the drop-in tan is kept open, rain-water and snow water will not accumulate in it.  Make sure that tightening bolts on the various parts of the tower, especially on the moving parts are tight.  As the cooling tower is installed on top of the roof, it is desirable to cover up the tower casing and the air exhaust outlet.