Hi,
Here is my experience after +20 years of dowsing.
Several old-timer's from Wa and Mt worked with me for years before it stared working. I was skeptical and at first it did not work. But later it started working little by little. One of the lessons I learned is not to get in a hurray, don't rush! But the most important lesson I learned was from an old Sourdough (93 yrs old) from Washington who had prospected and mined all over Ak, Wa, Nv, Az, Or. He told me very sternly, "Never dowse for greed, dowse for need!"
Over the years I have mainly dowsed for prospecting and have found several nice mineral prospects (copper, silver, gold...) along the way.
Dowsing does work, but I have also found there are a lot of factors that go into it and a lot of unseen factors that can really mess you up. An old-timer in Montana I worked with told me a story of digging a 30 foot prospect pit on a strong gold signal he got only to break into an old stope below. Thankfully, he was tied off so when the thin layer of rock at grassroots collapsed into the stope below, he was able to scramble out just in time.
I recently dowsed for a well for myself and everywhere I went on the property showed water a 6-7 feet. I knew it couldn't be shallow because I had already dug down to +7 feet in one area and all I found was heavy, saturated, clay-sand mix from 4ft down. I finally hired a driller and gave it my best guess. He hit heavy, saturated, clay-sand mix from near surface to about 65 feet where he hit a 15 foot thick layers of heavy, wet clay, before finally punching into fractured bedrock and water at 120 feet.
I have noticed similar interferences in prospect-dowsing where a specific rock layer will mask a vein. I now realize this is a similar situation because the multiple clay seams acted like barriers to the "signals" water creates as if flows through the ground beneath our feet. If it was just soil or gravel or even rock, no problem, but clay is like a "wet blanket" - it inhibits the signals from coming through, especially 15 feet of it.
The best way I can explain dowsing is it works just like modern day geophysical surveys. But, instead of a magical black box hooked to all kinds of sensors laid out on the ground for 1,000's of feet, one's body acts like a receiver and can provide insight into one area at a time. The cool thing with the geophysical surveys I have worked with in the past is they can give you a pretty picture of a large area, whereas dowsing is basically just of the area where you are standing and then you have to connect all the dots - like several posts here have mentioned.
Every time I dowse, I learn something new...So enjoy it and don't stress so much as to how it work, but what you can learn about the area you are dowsing. And remember, "Don't dowse for GREED, dowse for need!"
Cheers!
Sourdough-Al