I'm sure most people are fine drinking water through their caravan water system - but having seen what was inside of a stripped down Whale pump, and blue pipework (always kept meticulously clean as per instructions), I stopped drinking the water through the caravan water system and always draw off drinking water straight from the site tap - tooth-brushing too! My alarming symptoms which always occurred when on holiday and just after we returned, and which involved extensive tests including brain and MRI scans never happened again!
It would be interesting to see some proper tests, though, of what comes out of a caravan water system in terms of purity, etc. I'm surprised that this does not appear to ever have been done - either by the manufacturers, or by a Caravan magazine or I can't find any published results.