I don't think it's the water that can freak them out, but the container that it's in. Chickens are a lot more afraid of strange new objects (especially big ones) than water. So if they react to the wading pool, it might be because of the pool itself, not because of the water in it. If the same...
I tried the sled method, but the chickens didn't like how slippery it was on the inside. They kept slipping and falling in the water and freaking out. So I got them a large planter dish instead, which worked much better. It's plastic, but a textured plastic that doesn't get slippery when wet. I...
Anybody can write a book these days. Books aren't what they used to be, so "I read it in a book" doesn't mean much anymore. The scarf was a good red flag. I would doubt the credibility of that book, too. Chickens are indeed afraid of water and can drown easily. Some are more afraid than others...