My grandfather was a huge believer in dowsing. We lived out in the boondocks and he used it to find water for their well.
He always told me that he only dowsed for need. If he felt like he was tired or not relaxed enough to dowse then he would stop. Either let someone else do it or wait until he felt that the answers were coming naturally. I can still see him walking slowly around the 3 acres they had looking for water. He went over it a few times to make sure and each time he got the same answer and they had water the whole time they were out there!
You can get a ton of information online about dowsing for water and go from there.
