The halacha is that you should only say a bracha on water if you're thirsty. All the seforim I've read agree on the following: if you're not thirsty, but you drink water in order to swallow a pill, you don't say any bracha before or after.
Let's say you swallow a pill with Diet Coke or another type of sugar-free pop. But such pop has no nutritional value. [Edit: Maybe the phosphoric acid in diet soda even removes calcium from your bones and teeth, and maybe the artificial sweetener even makes your pancreas wrongly release insulin into the bloodstream. So maybe diet soda even has negative nutritional value.]
Should you say a bracha on the drink beforehand?
Please cite sources.
I couldn't find an answer to this question online. I seem to recall that The Laws of B'rachos by R' Binyomin Forst (ArtScroll) includes a discussion of when blessings are necessary before food and drink, and when they're unnecessary. But I don't remember exactly what R' Forst wrote.