There are over 60 thousand Mosques spread across the Kingdom of Saudi Arabia, consuming nearly 3 Terawatt-Hours of electrical energy, 70% of which is due to the use of mostly inefficient HVAC systems. Additionally, Mosques consume large amounts of water, as prayer requires ablution; the act of washing exposed body parts in preparation for the prayers. It is estimated that nearly 7 billion gallons (26 million M3) of mostly expensively treated water is used annually for ablution, 50% of which flows directly to the drain with very little contamination. This water usage in such a severely water stressed country, coupled with the fact that electricity consumption has been steadily increasing by nearly 8% annually for the past 10 years, makes it imperative to adopt innovative ideas not only to use water effectively, but also to find ways to control power demand growth rate. This paper evaluates the potential savings in water and energy, from reusing ablution water to run mosque air-conditioning systems, using high efficiency Indirect/Direct Evaporative Cooling (IDEC) technology. The water consumption footprint of the IDEC system, in different climatic conditions across the country, was assessed and compared against the amount of local mosque ablution water availabilities. A comprehensive site-to-source water-energy nexus is presented, including installation and health challenges of this innovative idea.