This is an off and on DOOM map I've been doing for some time, basically whenever I get bored. You might recall a previous showcase of it where I made an 'auto-doc' terminal to heal the player.

This is another part of the level, the water pump. This gif doesn't make it as clear as I'd like but basically the intended effect is to make you think that you've drowned the imps in the tank, while also raising the water level of another part of the map to allow you to traverse it.

To create the effect of the water rising, it's a simple 'make floor go up' effect but the difference is how you handle the textures on the side. Textures set to 'pegged' will move with the geometry IE go up with the floor or down with the ceiling. But textures set to 'unpegged' won't move at all, even as the floor or ceiling rises or falls. By making the side texture on the water unpegged, instead of looking like a solid 'cube' of water is rising out of the ground, it gives a more convincing effect that the water is actually 'filling' the tank. But that's not the only place the effect is used in this scene. Way in the back, to create the effect of that computerized bar rising with the water level, I simply made an extremely thin, second bar and put it right in front of the other, nestled into the floor. Then when it rises, utilizing the unpegged effect, it makes it look like the red bar is 'filling up' the yellow part. From a distance, it appears to be the same 'screen' but in reality it's just a red set of lights rising in front of a yellow set.

To better sell the 'drown' effect, the imps are pushed up out of sight of the player. In reality, they're being crushed to death against the ceiling and the floor (there's no true 'water' in DOOM, merely floor textures made to look like liquid, it wouldn't be until 1994's Heretic that the engine would even get the first effect of 'sinking' a little into the water when you stand on it).