How would I go about simulating waves with purely Y movement

Normally, I would give a script that I tried to attempt this with, but I have 0 clue where to start, I am trying to makes waves

pictures here.

And I only wanna go about making the water change by moving it up and down on the y axis, but im terrible at cframe and timing and math, but want it to go up fast and down slowly and then repeat after like 4 seconds, so I was wondering where to start? thanks