I haven't personally heard of an ECU (Honda or otherwise) that survived
getting wet. My son's '89 (?) Accord he had in Washington state got about an
inch of water in the floor during a flood and the ECU was severely damaged,
although the engine still ran after a fashion. It drank gasoline like crazy
and the "check engine" light stayed on. More commonly, flooded ECUs just
fail completely. A replacement from a wrecking yard is the obvious solution;
his was $75 although others can cost over $100 US.

FWIW, back when I worked in avionics a navigation system was brought in by
an insurance adjuster because the pilot said it failed in heavy rain. I
worked on it as he watched, and sure enough the first thing we saw inside
was heavy water spotting, starting at the cooling fitting. But why was it
dead? All the boards were coated with urethane. I found an open circuit
board trace in the power supply. On very close examination (good light and
magnifying glass) we could see there was a pinhole in the coating and where
that hole in the coating was the trace underneath was gone. A piece of wire
soldered across the gap and a swab of urethane made it as good as new... and
it left me with a new respect for the corrosive power of the combination of
water and DC.

Mike