WaterSense labeled fixtures obligatory for Indoor water use reduction

To best answer your question, water sense labeled fixtures (or equivalent) are not obligatory for credit WEC2. It is required only for the fist part of WEP2,the prescriptive path where all fixtures must show 20 % or less water use reduction.If all the fixture could'nt meet this threshold then you have the second path, the Usage based calculation where thru Indoor Water Use Calculator you demonstrate that 'in aggregate' you meet the 20% reduction.This efficiency from fixtures has to be complied in the prerequisite. This savings from second path is extended to the credit WEC2 where you increase the percentage reduction by using alternate non-potable water sources and get points.