I have a 1x1 waterfall (I use it in a chest room to climb up and down and access lots of chests).  As long as I'm only barely touching the water I did not used to lose breath but could still climb the water.  As of snapshot 20w22a it now causes me to lose breath bubbles as soon as I'm touching the water at all.  The only way to restore breath is to leave the water stream completely and fall to the ground.