How to prevent water to leak through walls?

Question

I have a stairwell surrounded by aquifer, and it's leaking in the level bellow:

I need to prevent this from happening.

Answer 1

Asked on the game discord, here is the solution:

If walls are dirt: dig and build a constructed wall instead [b-n-l]:

If the walls are stone, smooth the walls of the staircase with [v].

Both of those prevent aquifer from dripping water.

Notes: aquifers can drip down through the ceiling if you dig out the level directly beneath them. Go one level further after you stop seeing damp stone.

Smoothing walls solution and safety level credits goes to discord user Schmee.