As long as you use deionized distilled water and don't soak the boards overnight to avoid moisture ingress, won't be really a problem for encapsulated devices like ics, caps or resistors, but could be for electromechanical devices, we had a lot of issues with -supposedly- sealed relays, in the end the only reasonable way was to add a post-washing fabrication step and solder them by hand.
I never felt ok watching all those tactile switches being washed, but I guess they will fail long after the warranty is gone
My company was a bit hacky about this, used normal tap water for the first "bulk" wash, removing all flush from the wave soldering oven and other hand-placed parts, then made a final rinse in distilled water and right away into the over for drying.