Where I worked, we used a PCB cleaning machine, that used an ion exchange resin to provide a supply of de-ionised water to wash the PCBs in.
However, because you put a detergent powder in the machine (just as you would in a domestic dishwasher), then the substance doing the washing is no longer de-ionised water.
Once the washing was completed, there was a rinse regime that used de-ionised water, and measured the conductivity of the rinse water until it fell below a certain threshold.
This process took a relatively short time, and was immediately followed by a drying phase, so presumably there was little opportunity for serious corrosion to take place.