Why and How dowsing works is not known. Dowsers cannot explain it; nor can scientists. I suppose anything that cannot be explained could be termed as magic. I think dowsing is natural, and has somehow to do with magnetism.
Over the yeas I have been consulted by many Construction Companies to find disused underground drains; underground spaces; and, of course, water. I once found a disused coal mine.
These were small firms that could not afford professional surveyors.
Anybody can learn dowsing in about ten minutes. I couldn't care less whether or not you believe it.