The HVAC system is the largest user of energy and water in typical commercial buildings. In the past, energy costs overshadowed water costs. Recent droughts and the need to expand municipal water supplies to support growth have led to increased water costs nationwide. Combined with the focus on water conservation in green buildings, the payback associated with reducing building water usage is greater than ever. Most commercial buildings use water cooled chillers to provide air conditioning because they are much more energy efficient than air-cooled chillers. Achieving these efficiencies, however, requires large quantities of water to operate a cooling tower. Most buildings also use re-circulating hot and chilled water loops to distribute heating and cooling throughout the building. Although not designed to routinely use water, these systems can use large amounts of water if undetected leaks occur. As the major consumer of water, the building HVAC system is an obvious target for water conservation efforts and often provides significant saving.