Aluminum composite panels are inherently water-resistant. The aluminum facings are impermeable, and standard PE / mineral cores do not absorb water, so the panel itself will not degrade, warp or rot from water contact.
However, they are not classified as flood-resistant building materials for permanent submersion.
Short contact with floodwater will not ruin the ACM sheet itself.
Risks come from trapped water behind the cladding: corrosion of aluminum/steel substructure, damaged insulation, mold growth.
Proper weather sealing, drainage gaps and weep holes are critical if used in flood-prone zones, to let water drain out from behind panels.
