Abstract: A humidification-dehumidification water desalination system uses a contoured interior chamber, essentially onion shaped, in order to balance the thermodynamics of the evaporation/condensation process completely by facilitating the needed fluid bypass with air and the contoured shape of the interior chamber so that the desalination can occur energy efficiently in a single stage humidification-dehumidification system. The contour of the internal wall of the interior chamber is loosely proportional to the differential of the percentage of water vapor that can be carried by air as a function of temperature, with the interior chamber being essentially symmetrical about a horizontal midplane through the interior chamber.