When I started working decades ago, we were taught how to use bent bits of fence wire to find underground pipes before digging
I literally found scores of pipes that way, and saw dozens of other people do it regularly. It was even taught at a local agricultural college as part of the horticulture course
Then someone told me it was a myth and doesn't work, so I set up a blind test with a hidden bucket of water and I utterly failed to find it
I was taught this too growing up in rural america. Did it myself at some land my grandparents had.
Best explanation I've heard for why it "works" is that when looking for places to first install pipes the location tends to be obvious or intuitive, so then years later when someone needs to find it again we naturally trend to the same rough area, pull out those stupid rod things and when they randomly cross there's a pipe there cause we're already standing in the general right spot. Get a high enough success rate and our brains start to think there is causation to the correlation.
Dowsing is a type of divination employed in attempts to locate ground water, buried metals or ores, gemstones, oil, claimed radiations (radiesthesia), gravesites, malign "earth vibrations" and many other objects and materials without the use of a scientific apparatus.
I had the opposite experience. Consistently derided and dismissed it as woo. Went to my parents' land a couple of years ago and my dad told me to try it. I didn't want to, that's how ridiculous I found it. But those things were moving in my hands in a way that had me halfway believing.
If something is tested and proven, it falls outside the realm of magic and just becomes normal everyday science or technology. It's like the saying about alternative medicine. Anything that is proven to work is just called medicine.
It's because the water does not flow in "pipes" underground. It is nearly everywhere, and so you have "found" it most times.. You just don't know at what depth you will find it - until you ask your neighbor :)