A study to examine the effect of evaporator diameters on the performances of a custom air-water generator had been conducted in naturally room air temperatures.  Performances in this study consisted of fresh water production, coefficient of performance, and total heat transfer from the air. The freshwater was attained from the dew that dropped from the evaporator walls. It was from water vapour in the air that condensed due to the low temperature of the evaporator walls. The evaporator which had dimensions of 285 mm x 12.7 mm x 480 mm was placed in an open box (top and bottom). It was made of copper pipes. There were three evaporators tested with different diameters. Case A indicated the diameter of the evaporator was 3.00 mm, Case B was the evaporator with a diameter of 4.00 mm, and Case C was the evaporator with a diameter of 6.35 mm. The results showed that the maximum fresh water obtained was 0.369 kg, the coefficient of performances found ranged from 7.8 to 18.6, and the highest total heat transfer was 152.1 W.