How does the Cistern work?

[SmokeSum]

I noticed when i first enter the room and go for first Valve next to the chamber that get filled with water, i saw a splash in the water...first i thought it was the water lurker so i trew a stone but no movement.
When i turned the valve the dark wind appeared and when i try to jump back i felled inside the water, first thought was like: SHIT!!! NOOOO!!!! but when i walked true the water nothing happend and i lost me sence of being afraid there, so i run true water like it was fun to do

BTW: What the hell is inside the chamber getting filled with water?