How can I detect if a certain part is touching a certain terrain (Especially water)?

Hi guys, I'm having a problem with the pathfinding service failing to find any path if a certain part of the NPC is submerged in water (No one seems to know the answer). so I thought of an idea which i will try but I will need to detect if a certain part is submerged in water, any one knows anyway of retrieving this info without detecting the terrain based on the Humanoid state.