Hi @disac Welcome to the Head and Neck Cancer group. Although you landed in a discussion about Ameloblastoma, a rather rare malady, maybe I can help you out.
Always feel free to start a discussion of your own rather than pop into another discussion. I know it can be a bit confusing initially. There are certainly people here who can help with many H&N cancer issues.
The radiation therapy can and often does take away our ability to speak. Voice requires the control of both the diaphragm and the vocal fold muscles. These vocal muscles can be weakened or stressed for a while. The fact that water sets off a cough is a good indication of some inflammation down there.
An ENT can take a quick look with a mirror to confirm.
I would bet cold water is worse than warm water to set off coughing. Many of us gargle with warm salt water or salt water with a little baking soda added. It helps.
These issues generally resolve themselves over time, weeks, even months because radiation is an injury to your good tissues similar to a burn. It takes a long time and is never quite the same when healed.
For me, taste came back slowly. Salt at first after three weeks. I lost taste for sweets but gained tastes for some foods I never previously cared for. All in all it took about a year for taste to stabilize.
Other issues might crop up such as nerve tingling, loss of bite control (biting your tongue or cheek) loss of saliva, etc. when they do, feel free to start a discussion or drop in on another appropriate discussion where other patients have had similar experience. Good luck and hope to hear from you.

@disac, I add my welcome. I moved your post to this related discussion so you can meet others managing symptoms after radiation treatment.
- How long before my taste buds recover after H&N treatments? https://connect.mayoclinic.org/discussion/taste-bud-recovery/

Disac, when was your last radiation treatment? Did you have any other treatments?