I've been told, though I've never had to follow through and make a study of it, that even fairly low voltage, if it somehow gets into the cardiovascular system can be quite injurious, at least in the short term, and that this is the reason most commercial labs keep the power supplies low in places people are likely to be inadvertently exposed.

Water is generally not so conductive, but, as you've experienced yourself, it can cause unpleasant effects.

Because it also can be conductive, it can, perhaps, influence what a potentiometer represents about its position. A strobe wheel might be a better thing to use. Those can be mounted on relatively water-tight bushings or even bearings, allowing for isolation between the innards and outside, which would be the user interface. A slider on an optically sensed strobe strip might be a possibility, too, wouldn't it.

RE