I didn't stutter. I was responding to a question of why would there be water tanks in the engine room.
Fact is, we don't know how the ship is laid out or where what is where. Kirk and Scotty could have beamed into engineering--which could encompass more than just the warp engines--or they could have beamed into environmental engineering, or even inside one of the nacelles, for all we know.
Flip a coin, though, I say it was somewhere in engineering to cover the bases...