Technically speaking we know the water table here is at 400 ft.
Many wells confirm that.
However I know of 3 properties that have great water at about 50 ft.
Next, in my home after 24 years I have water in my sump that I never had previously and I am sure that it is pure usable consumable water.
Must add however that we are lakeside and have multiple springs that feed the lake.
In my case I am sure that when I built that I actually cut off a surface spring that flowed into the lake and with time it simply re routed itself into my sump.
As to dowsing, well good luck. but the do U still believe in Santa Claus?
I'll bet many well diggers will suggest a dowser that for a fee will locate U a water source but I'd look for another driller, one that really knows where the local water table is.
Shucks lots of gov't sites have all that info on line, not rocket science nowdays.