It’s almost as convenient now, albeit behind a different button: press once on the side button to bring up control center. You should find water lock there.
What’s more annoying, I’ve found, is that end workout now requires two button presses. End and yes, really do end workout. 🤦♂️
I don’t understand this decision, they removed the conveniently placed water lock button to replace it with an empty space. I had the same issue when I couldn't find it, just to learn it’s somewhere hidden in my control center.