I play on survival / peaceful most of the time. I have a helmet that I've always used to build underwater. It has respiration III, aqua affinity, and something else that doesn't come to mind at the moment. Playing on peaceful with the helmet allowed me to stay underwater indefinitely. My health would heal within a second of being damaged from drown damage. Now since Update Aquatic my health doesn't generate fast enough and I can die pretty quickly.
Anyone else having this problem? I hope they didn't break respiration. I do a lot of underwater building but I won't anymore if this is the new norm.
Could be a bug or they may have changed the drowning damage/peaceful regen.
There are a few ways around this. Water breathing potions (they can last up to eight minutes), or set up a conduit (once its available). If you had a beacon with regen that might be enough to overcome the drowning damage (I've never tried it so not sure).
You could also set up places around the build that have air and duck in there once in a while.
As the game changes it is sometimes necessary to change with it.
I think the damage is done in three quick shots, then a pause, then repeats. It's not the slow single damage like before. This does add a new challenge to the game. I was mining and dug straight into the side of an underwater ravine. It took several minutes of swimming around and digging breathing pockets to find my mineshaft to get out. It didn't help that it was under a Mushroom Island and the water was tinted.