Thanks. Yes. it is part of observable entity. I'm specific to capture types of fluid and quantity intakes.
I see SNOMEDCT codes like-
SCTID: 364659006 - Measure of oral fluid intake
SCTID: 251853006 - Oral fluid input
SCTID: 301896005 - Time of last oral fluid intake
SCTID: 733908002 - Oral fluid offered
But nothing specific code in FHIR Observation resource.