; or (B) a FEMP designated product. A WaterSense plumbing product should preferably, when possible, be installed by a WaterSense-certified or, if WaterSense certification guidelines do not exist, licensed plumber or mechanical contractor, and a WaterSense irrigation system should preferably, when possible, be installed, maintained, and audited by a WaterSense-certified irrigation professional to ensure optimal performance. (2) Exceptions The head of an agency is not required to procure a WaterSense product or service or FEMP designated product under paragraph (1) if the head of the agency finds in writing that— (A) a WaterSense product or service or FEMP designated product is not cost-effective over the life of the product, taking current and future energy, water, and wastewater cost savings into account