How many times has this happened to you? You're setting up an artificial underground beach for your dwarves, by draining the sea into a tunnel that flows into an open cavern, when suddenly half your population (Including several legendaries and most of your military) are drowning with no hope of surviving. And then you're invaded by a dragon, because sure, why not?
Or how about the opposite problem? You've created an elaborate execution chamber that drowns prisoners using water pumped in from below, all so you can stare at the abstract symbols on your screen and imagine their eyes locked on the floor drain silently begging you to release them while you cackle with unbridled glee. Only the water never comes, so now you've got to drag the elves out of the slightly damp "drowning chamber" where they've been playing "20 Questions" for several weeks (The answer is always "tree" because elves are terrible at "20 Questions".) and take them to the dropping cliff like some kind of savage.
What I propose is an alternative water display, one that informs the player how many levels a pressurized "7" of water will attempt to rise without a ceiling. So in its normal depressurized state it would read "0" with another magnitude added for every level the water will need to rise to once again be depressurized. That way, the difference between the highly dangerous water main from the surface and the normal drinking pipes that you're looking to expand becomes immediately obvious before you kill everyone.