We wish to meet the intent of WEc1.2 by irrigating entirely with non-potable water. To do this, we will provide on site storage for rainwater and/or groundwater from the basement de-watering system. The storage will be sized to provide irrigation for the project in all normal years. However, in drought years, if the tank does not fill up with enough water to meet our irrigation requirements, we would like to have a backup system that relies on potable water. Note that if groundwater is used (and we may rely entirely on rainwater storage, depending on the outcome of our study of groundwater volume to be conducted this summer during the dry months), it will not be "potable" as it could not be used for drinking without a well permit which is difficult to obtain and will not be sought for this project.We propose to document the plant types, the irrigated area, and the typical rainfall (or groundwater volume) for a "normal year," along with the catchment area and the storage tank size, to show that we have designed a system that can provide for all our irrigation needs in a normal rainfall year. Please confirm that this strategy meets the intent of WEc1.2, even if it is connected to a potable water system for backup in drought years.
Capturing rainwater for irrigation purposes is a commendable approach to eliminating potable water use. Likewise, according to the WE c1.2 7/10/2003 CIR ruling, irrigating with water diverted from a basement de-watering system is acceptable, but should be explained in a credit narrative. Thus, the described approach meets the intent of WEc1.2
The approach of designing rainwater storage for a "normal" rainfall year and providing potable water as backup is acceptable as implied by the LEED-NC Reference Guide calculations section. Alternatively, the most effective approach to achieving this credit is to landscape with drought-tolerant plant species. This strategy could potentially eliminate the need for potable water backup during extended dry periods.
**Update October 1, 2013: This ruling has been made applicable to WEc1 in LEED v2009.