I don’t know how the Dutch generate their potable water but reverse osmosis and flash evaporation of seawater are safe processes for drinking water generation. Water contamination usually occurs at the water storage facilities.
So why would Dutch water storage facilities suddenly be contaminated with cholera?
Here ya go:
https://en.m.wikipedia.org/wiki/Water_supply_and_sanitation_in_the_Netherlands
Holland is a modern country with a clean water supply. Why in the world would they have a cholera outbreak?