Dementia had aspiration, must have water to be thickened for him to drink. reasons? what is happening to the esophagus, trachea, etc for this need?

Ask the dietitian: The staff at the facility will be able to help you understand these things if they have permission to discuss things w/ you. Generally, the thickener slows the fluid passage and makes it less likely to choke. The nerves and muscles are just not working well - causes can vary. That area shares the eating/breathing functions and when impaired it is tricky.