What goes to this water pipe

Hi guys I'm in the middle of building my sr20 back up after a year of it being stripped I'm just a little stumped what goes to the little pipe that comes off the main water pump pipe any help is appreciated
Https://imgur.com/a/rCbbY
Https://imgur.com/a/g04Kc

heated throttle body or the wax stat under it would be my guess.

As above, connects to the throttle body.