Originally Posted by KingOfFleece
The bucket test will expose faulty seams in a hurry.
A good garden hose will do a good job in lieu of a rainstorm.
I have several SCUBA dry suits with zippers. They don't leak at 100 feet down which is WAY more pressure than we see on our bikes. Zippers should not leak.
The water resistant zippers used in moto gear is not as robust as the dry suit zipper. It is basically a reversed coil zipper with a coating on the zipper tape, and it is very easy to split the "seal" with any sort of tension across the zipper. Once you play with it, you will know exactly what I am talking about.
Something like this is enough to allow water to seep through.