I imagine his thought process is something like, "if I could douse for water, then I am more justified in my belief that the Book of Mormon and other magical things are true."
Here's his infamous first hand-account of water dowsing from 2015:
DP wrote:I found water running through a buried pipe of which I was unaware. I didn't even know I was looking for anything.
I was simply told to allow the two metal rods free play.
They crossed at a certain point, then uncrossed. It was very distinct.
Only after repeating that several times was I told that a clay pipe ran under the floor right where the rods crossed.
I had several other people undertake the same experiment throughout that day. With one exception, they all had the same experience. (The one exception was a big burly mechanic with huge hands. I suspect that he didn't allow the rods free enough movement.)
I wasn't expecting what happened. Nothing in my worldview predicted it. It didn't fit my scientific notions, and nothing in my beliefs depended on it happening.
Yet it happened.
I found it very strange and unsettling.
https://www.patheos.com/blogs/danpeters ... 2188051209
The comments from Reddit are pretty great:
https://www.reddit.com/r/exmormon/comme ... uccess_at/
His approach to dowsing apologetics is the same as his approach to Mormon apologetics.
"You may not like my unsupportable claims, but I know what I've experienced, and I don't care to know if I'm wrong. But I will treat you with unbearably supercilious snottiness if challenged."
I don't fault Peterson for having his experience with the dowsing rod and thinking, wow, something is going on here. But unfortunately, instead of investigating and applying scientific principles to really figure out what is going on, he doubles down on defending that "something" as being real. The scientific method is counter-intuitive. We live our lives according to our lived experiences, by anecdotal evidence. The scientific method gives us a way to step outside our biases and test our assumptions. Most water dowsers probably aren't intentional frauds, they sincerely believe in their abilities, even in this modern enlightened age.