Though I haven't been on any of the CP water rides in years, these are a few of my observations through the past few years.
All three are located in Frontier Land.
There are 'drying pods' that can power-dry a family of 4 for $5 for a few minutes.
My husband and two friends went on Shoot the Rapids, then spit the cost for the drying machine. They had to run it twice before they felt really dry. An hour later, the one female and both males were still complaining about dampness in regions that don't dry too quickly.
If it is a hot day and you don't want to wait a long time for Snake River Falls to get wet, there is a bridge folks can stand on right where the raft plunges into a soaking splash. I haven't been on it or been near the bridge for a few years, but as I remember, anyone used to be able to stand on the bridge to get soaked.
Never been on Thunder Canyon. Just too wet for me and never wanted to bother with paying for a body dryer or locker.
However, the body dryers or nearby lockers are ideal if you want to do the water rides inside Cedar Point (separate from Soak City). I've seen many use the body dryers and many have a full change of clothes in their backpacks that they stow away. Restrooms are nearby the water rides and corresponding lockers.
The last time I used a locker was in 2006, key entry and was $5. Now, I saw that you have to go to a kiosk in the center of the lockers, swipe a credit card, and get a code on the receipt. I have no idea how much it costs now.
Just giving somewhat of a 'heads-up.'