Reducing water used in irrigation can conserve scarce groundwater resources, and generally reduce demand for potable water that is becoming scarcer in many parts of the world.
However, the construction costs of water-saving systems are likely to incur premiums, particularly for more sophisticated rainwater capture and graywater treatment systems.
Additionally, LEED v4 requires water metering (manual or automated) to cover all potable water uses for the associated grounds on a monthly and annual basis, which represents an added cost. Note that water metering costs can be greatly reduced by being spread over the whole cost of the Building Automation System (BAS). This is not reflected in the estimates below. 
Cost Synergies
SSc2: Site Development—Protect or Restore Habitat
SSc3: Open Space
SSc4: Rainwater Management
SSc5: Heat Island Reduction
WEp2/c3: Indoor Water Use Reduction
WEp3/c3: Water Metering
