Since part number 16100-80008 is discontinued from Toyota, I've found that Aisin WPT 168 is supposed to be the direct replacement water pump fer the 1NRFE engine. About $70-$76 plus shipping. 
I'm not sure if the 2015 Scion iQ has a different water pump or not.
Amazon.com: AISIN WPT-168 New OEM Water Pump Kit : Automotive
Buy AISIN WPT-168 New OEM Water Pump Kit: Water Pumps - Amazon.com ✓ FREE DELIVERY possible on eligible purchases
www.amazon.com
I'm not sure if the 2015 Scion iQ has a different water pump or not.
