Medically speaking, thirst was probably not the most important thing for Jesus to be concerned about. He was dying on a cross. If He wanted to improve His situation, not dying on a cross would be a better place to start.
I work with people who have a lot of problems. My wife often deals with people who are dying. There are times in both of our jobs when we will come to a point where we realize that there is nothing left for us to do, medically speaking. Whether it is a terminal condition or a severe and persistent mental health diagnosis, sometimes people just are not going to get better. So what do you do?
Priscilla believes deeply in the importance of making dying people just a little more comfortable -to improve the quality of life, no matter how short. Jesus seemed to have a similar opinion. Knowing full well that every person He healed would someday die anyway, Jesus spent much of His time on earth making this temporary life just a little more comfortable for others.
We all, like Christ, are terminal cases. Time making another person a little more comfortable is well spent.