I remember having problems with leakage on a board that
stored voltages in polystyrene capacitors using CMOS
switches and op-amps, but the voltage would bleed off too
quickly to be useful as a "memory". We tried all sorts of
flux removers and it still didn't work well enough. But I had
had an idea that it might be ionic contaminants such as
salt, so I took a board into the mens room and scrubbed
it with hand soap and flushed it with hot water. Then I dried
it with a heat gun, and "voila" it worked like a champ rather
than a chump.

Interesting observation.

Question... Wouldn't distilled water alone flush off ionic contaminants?