Water witching and dowsing
Water witching / dowsing is full blooded demonic, and is spiritually dangerous. This is one of Satan's 'practical devices' used to lure people into his kingdom and gain access into their lives.
Much of the time, those who practice this will use a piece of wood, while others will use coat hanger wires. They claim that only certain people have the 'ability' to do it. If there was a scientific reason, then anybody could do it! Some can only use wire, while others can use wood but not metal, others can even use specific kinds of wood and not others! One man may be able to use cherry wood while another oak, but they couldn't swap sticks and still do it.
Don't be deceived, it's occult power behind this practice, just like a Ouija board. Even though the Bible doesn't specifically speak of an Ouija board, doesn't mean it's a harmless toy. It's still occult, and the Bible makes it clear we are to have nothing to do with the occult.
"But it's practical!"
It doesn't matter if it's practical or not. Many could easily argue that spells are practical too, because they tend to 'get the job done'. Demonic power can fake healings, tell fortunes, etc. to get people to take the bait. Some think it might be practical to know their future so they can better plan for it... seems practical and useful, right? Wrong. Such an action defiles a man and opens the door for demonic spirits to enter. It gives them legal grounds in our lives.
We are warned that Satan is out in full force to deceive us through signs and wonders that seem 'practical' (how else could they confuse the elect, if they didn't seem beneficial and practical?):
Matthew 24:24, "For there shall arise false Christs, and false prophets, and shall show great signs and wonders; insomuch that, if it were possible, they shall deceive the very elect."
2 Corinthians 11:13-15, "For such are false apostles, deceitful workers, transforming themselves into the apostles of Christ. And no marvel; for Satan himself is transformed into an angel of light. Therefore it is no great thing if his ministers also be transformed as the ministers of righteousness; whose end shall be according to their works."
Don't be fooled, Satan has given great fame and wealth to those who have sold their soul out to him. Money seems practical, right? Not when it costs you your soul.
It's just not scientific
If there was such a thing as 'reactions to positive/negative poles', etc. as some believe, then we would see things flip flopping all over the ground for no apparent reason. You would be carrying a coat hanger out to your car, and all of a sudden, it would want to pull down towards the ground! Children would be playing outside and their toys would start moving on their own just because there's water below them. How come fishermen don't have their fishing poles going crazy when their poles are hanging over a river? Why does one person have the ability to water witch when another person using the same exact 'style' (excluding the spiritual ability) could stand out there all day with no results?
If it has something to do with something being 'charged' negatively or positively, then why do some use pieces of coat hanger wire, yet others use Y shaped wooden sticks? On top of that, some people can only use cherry wood, while others use oak. Why can't the person who uses cherry use oak as well? The next person could use oak but can't do a thing with cherry! It makes no logical or scientific sense whatsoever.
A similar practice... occult levitation: Trying to scientifically explain this is like trying to explain the time when I watched some boys move a huge potted tree when NOBODY was touching it... it was moving on it's own. Or the time when somebody was lying in their bed, and looked out their window to see a Satanist floating in the air... up to a window on the 2nd story of their home! It's called levitation and it's very demonic. People use it to make their bodies float in the air in the occult/Satanism world. Demons are not limited to floating bodies around the air, but also objects such as books, etc. They can even make an object seem so heavy that 5 in shape men could not left a simple small 25lb coffee table! Clearly demons can lift things up or push things down.
Seeking occult power defiles you
The Bible warns us that we don't even have to be the one doing the work... all we have to do is seek those with occult power and we become defiled ourselves:
Leviticus 19:31, "Regard not them that have familiar spirits, neither seek after wizards, to be defiled by them: I am the LORD your God."
I had at least one person in my family tree who had occult power (which was obvious in other areas of their life) and they had no problem whipping out a stick and making it move above a vein of water.
I've even heard of somebody who used to have the ability to water witch, but after he came to Christ, the spirit left him and he was no longer able to do it. Even though it doesn't always work like that (the auto-shedding of evil spirits), it is quite possible for people to 'shed' spirits when they come to Jesus like that. Obviously, this man lost the demonic spirit that was giving him the ability to watch witch.
If something has the makings of being occult, I wouldn't touch it with a 10 foot pole. The Bible strictly warns us against involving ourselves with the demonic realm. It's a great way to open yourself up for evil spirits to enter.