Special needs child issue with fluid intake after procedure Looking for advice and/or water bottle suggestions

My son is having his adenoids and tonsils removed on the 29th. He's going to be be 4 next month. He has multiple delays ( hasn't been officially diagnosed on the spectrum but has many sensory issues) included feeding. As it is, hes not great at fluid intake. He drinks from a no split straw cup . Im terrified about his fluid intake after the procedure. Anyone have similar fears and issues ? What helped ? So scared.