Sorry kinda at a loss here with no error message popping up my guess is MiSK is just not working but don't really know how to solve it.
on join:
while player is online:
block at player is water:
damage player by 5
if block data tag "waterlogged" of block at player is true:
damage player by 5
wait 1 second
That could work but I don't really have a way of testing it rn it requires SkBee tho.