Water levels

Sorry for posting so frequently, but I have one more question...
Im trying to make water rise over the course of 1 block. There are the usual water levels aka hights, so Im just cloning a certain height of the water block over to the floor. For some reason tho, its glitching out and bouncing around. I think it has to do something with it not having a source block, so it tries to dry out each tick before its cloned again...
If anyone has any ideas how to animate water rising over 1 block, I would really appreciate to hear them 😅 TY