Canopy deteration occors for many reasons. Water, Sun (UV light), dirt, Just the basic use of the parachute. Water damages the parachute because as it dries the different materials (the ZP or F1-11, the Load tapes, Lines, and Stiching, etc..) will expand and contact at different rates. This can cause the parachute to be slightly deformed. This is even more pronounced if dried quickly ie, in the sun or by direct heat (Ive seen a hair drier on HOT being used). It is estimated that for every water landing you have is equal to 4 or 5 dry jumps. I am speaking directly of FRESH water, as SALT water is even more degrading.
nic