The game says I still have one secret to find at Washington Institute, so I found pagb666's walkthrough and he just walks up to this water dispenser and can shoot it. It also looks different (has glass around it) compared to my version.

Apparently no additional steps should be necessary - I should be able to destroy the bottle (but it's not there in my game, just a floating water block).

I've attached a shot of how it looks here.

Is this a bug in GOG or Linux version?

might be a linux issue, my gog copy def has the glass and shooting it works.

Actually, I just went to chapter select and went there again - the glass is there when first entering the building and I can break it just fine.

So it must be something else I did that removed the glass without breaking the whole dispenser...

I tried letting the guy with the bow shoot it and that also worked. I tried quicksave-quickload and that didn't break it. Another idea would be to play through the whole thing and periodically check at which point the glass disappears (if it ever does), but that's too much work ;) I'm still curious though! If anyone figures this out, please let us know! :)

Have you tried using an Eduke compile ?