Municipally supplied "purple pipe"

Municipally-supplied non-potable systems qualify for WEc3 credit but not for meeting WEp1 (see USGBC's Additional Water Use Reduction Guidance - page 4: http://www.usgbc.org/resources/water-use-reduction-additional-guidance). So your fixtures need to be efficient enough to meet the prerequisite on their own. But you can then get points based on the actual reduction in potable water use. From my experience, we document just the fixtures without any purple pipe water in the WEp1 Credit Form/calculator. We then select the Special Circumstances option on the WEc3 Credit Form and upload a separate duplicate version of the calculator which includes the purple pipe contributions for the WEc3 compliance/point thresholds.