The warning being that if you ignore the warning, or try to hide it (ground in the water), that “next time, it won’t be a warning”?
More seriously, can’t reinforce what @Stroonzo said enough. Fix the problem, don’t hide it. Adding a ground to the water is hiding it, plus there is enough resistance to the water that you can’t actually ground the whole mass of it.
Are you not utilizing a GFCI on this branch circuit or receptacle? The current differential neutral to hot caused (and felt) when you touched the electrified water should have instantly been detected by a GFCI (disconnecting the line).
There may be more left to resolving this than replacing the submersible pump. That is, the installation (or replacement if faulty) of a GFCI.