You are not going to feel the shock when you just stick your hands in the water -- because you are probably wearing rubber soled shoes. You have to stick one hand in the water and one hand on the ground to complete the circuit. Now, I am used to getting shocked in water all the time at work, so it doesn't bother me, but if you are not used to getting electrocuted, use your voltmeter instead. I'm sure you've gotten shocked before, it's just more of a "surprise," but you can avoid it if you want.
Mine were getting shocked from their heated bucket when it was plugged in -- the bucket was fine, the outlet was fine. The problem is, the only outlet is the same one the farm's MASSIVE (100 mi) fence charger was plugged into plus both the ground wires. There's just so much power in that corner, it was overwhelming the shielding on my extension cord which was then carrying the pulses of bleed-off power to the water. So I gave up (I could have gone all redneck and tried pipe insulation, but I had redlined my give-a-sh*t meter) -- we use the big troughs in winter and only the top freezes and staff removes ice every day, so they will be fine. They like the warmed water, but hey, I like pretty shoes and I can't afford those either, so too bad.
I was able to tell what was going on by sticking one probe of my voltmeter ($20 at Autozone and endlessly useful; just make sure you put it on the right capacity setting for your voltage so you don't blow it out) in the water and the negative in the ground (lick the negative for a better ground if your soil is very dry, moisture helps) : the pulses of power exactly matched the clicks of the fence charger. Voila!
I've had the problem for years, but it was not a result of faulty wiring or grounding issues. The big overhead power lines border one section of my property -- and they throw stray voltage. The pastures closest to the lines have more stray voltage than those furthest away from the lines.
My local power company resolved the problem by installing what is called a Ronk Isolator on my transformers (at no charge), which solved the problem.