A system for cooling an outdoor space comprises a main cooling module, a heat rejection module, a water management module, and a control module. The main cooling module comprises an indirect evaporative cooling unit for pre-cooling an intake ambient air to a lower temperature by reducing sensible heat, and a direct evaporative cooling unit having a first evaporative medium for cooling the pre-cooled air (or direct ambient air) through vaporization of water thereby generating a conditioned supply air with a much lower wet bulb temperature than the ambient air. The heat rejection module comprises a second evaporative medium for removing heat contained in the excess water from the indirect evaporative cooling unit thereby producing cool water having a temperature almost equivalent to the intake ambient air wet bulb temperature.