Toddy.
Ok, I took that one personally, and I shouldn't have. My apologies.
And no, you don't always offend me. Rather the contrary actually, on the whole. This one just happens to touch a nerve. I'm not against an open mind, just irrational thought.
Oh, and I have tried dowsing, actually. My scepticism is based on personal experience as well as logical thought. Logical thought tells me it shouldn't work. Experience reinforces that by showing me that it doesn't work. And before anyone says it I tested dowsing during a period of my life when I was a great deal less sceptical than I am now. I really wanted it to work.
Ok, so it has been claimed that dowsing works. Let's proceed on the basis of looking for an explanation of how it might work.
Pieces of bent metal
In order to 'detect' anything, you need to have some sort of sensory system. Metal is just metal. No sense organs or strucutres of any sort. It doesn't matter what shape you bend it into, it can't detect anything. Certain metals will respond to magnetic fields, but it would have to be an enormously powerful one to get a noticeable reaction. Water isn't capable of doing that. Finally, even if somehow, by means unknown, the bits of metal could detect the water, there is no mechanism by which they are capable of sudden and spontaneous movement, other than by gravity.
Ergo: bits of metal cannot detect water
The hazel twig.
This has been cut from a living thing. Therefore it is dead. Any sensory structures it might have are now also dead. However, plants are known to be resilient, so lets say we have a freshly cut bit of hazel in which the tissues are arguably still alive. Ok. Now, most of a bit of wood like this is made of lignified cells (wood, to a layman). Lignified cells are dead, even in a living plant. The living cells are in a layer just beneath the bark, but in a branch or trunk these cells are concerned almost exclusively with the transport of fluids within the plant. They are not equipped for detecting anything external to the plant. Granted, there are pores, but these are for transpiration (regulating the rate of water loss, and some limited gas exchange) and have no sensory capacity. Finally, the living cells are, except for the pores, covered with a layer of bark, which is made of dead cells. There is no way that the hazel twig, even if nominally alive, can detect water. Finally, just like the metal, it isn't capable of sudden and spontaneous movement either.
Ergo: the hazel twig (or any other wood) is incapable of detecting water.
What does that leave?
Well, on the end of the bit of metal or hazel twig is a human being. Alive, and equipped with a full array of functioning sensory apparatus for the purpose of detecting and analyzing the world around it. Humans have the capacity to detect changes in temperature and humidity, and to perceive differences in soil type or the distribution of plants, all of which may, consciously or sub-consciously indicate the presence of water to the human. Furthermore, a human being has a muscular system enabling it to produce sudden mechanical responses to stimuli received. Now we are at least taking about something possible.
Since I mentioned subconscious perception, let me clarify. It has been well established through monitoring of brain activity that the human brain is capable of responding to stimuli well below the threshold of conscious perception. For example, if I find the quietest sound that a person can hear, and make it a little bit quieter, the person can no longer consciously hear that sound. If I then make that inaudible sound 100 times quieter again, the auditory centre of the brain will still produce a response to that sound, even though the conscious brain is not aware of it.
So, I'm still a dowsing sceptic, but if I wanted to know how it worked, I would investigate the person, not the paraphenalia.
All the best,
Mike
and if that's so then we'll never suss it out properly, since we're all unique, and maybe the old dowsers are right and some folk will never manage to do it 
