Normally an exact number would be hard to come up with, but not in this case as I know of exactly none who have shown that ability to others (based on my personal observation and Googling. Under controlled conditions, that is.) I'm prepared to bet my caravan against your house that that's the EXACT number you know too!
Being committed and getting off your arse every weekend doesn't make throwing knucklebones an effective form of futurology or dowsing a real phenomenon.
"Beats sitting in your armchair or looking at a computer screen and googling away to gain your information from like many do!"
If that's a dig at me so be it but you should know I've been interested in dowsing for many, many years since before Bill Gates had a pot to piss in and I do know a bit about it! As does George. Why demonise us (which is what's coming across loud and clear)? Don't you think we'd RATHER it was proved to be a real phenomenon? You'd have to be bonkers not to wish it was.
Just sticking to my 1,000's of dowsers out there, lets, just for arguments sake, say there are 5,000. I doubt very much that more than 50 dowsers have been 'lab tested' to prove their apparent claims, or more likely, asked to prove something dreamt up by their examiners.
Would you seriously consider that the 'failings' of those 50 dowsers (1%) are truly representative of those other 4,950 who have not been tested? It would only take 1 out of those 4,950 to pass the tests asked of him to prove that dowsing does work, but not for everyone! That is your weakness, you make no allowance for the possibility that it may just work!