I was trying to make the point that, in the KCN case I posted in the first post of this thread, the reaction does not occur not because all alkyl halides are (wrongly) insoluble in water- and in fact some alkyl halides do undergo spontaneous solvolysis in water- but because the alkyl halides would prefer the organic solvent in preference to water, for entropic reasons. This point was never raised.
But if we directly dissolve the same alkyl halide in water and raise the temperature to moderate levels, the reaction will occur, even if a bit slow.