Neither do I. I looked into the mod's files and found the recipe for the "water-bomb" and it requires electric motor and the green circuit(4th circuit in bobs/angels mods). I do not see a tech requirement listed.
I was able to give myself a water-bomb, so I assume it is unlocked later?
Edit: after removing the mod loading the game, closing the game, re-adding the mod, and restarting the game, the water-bomb now shows up under Combat tab, when using Bobs and Angels mods.
