As an attempt to fix the extremely common partially flooded caves in 1.18 Experimental Snapshot 2, Partially flooded caves were made too rare in 1.18 Experimental Snapshot 3

As an attempt to address a problem with snapshot 2 where water caves were too common, they are now made too rare. Many players have rarely encountered one. All that's left now is aquifers.

Strangely, water filled caves are now most common around y=0

I have attached a picture from Henrik's cavegen prototype video that showcases what a partially flooded cave looks like.