FAQ on Film Water Damage by Mick Newnham
Source: The Association of Moving Image Archivists (AMIA)
Film that has been immersed in water is in severe danger of having the base separate from the emulsion. This means that the part of the film with the image on it will come away from the plastic backing that gives the film its shape. The film is also at risk of being contaminated by mold growth and debris from flood water.