ultimate leak test
My backpack has this external pocket where I place my big-mouthed Nalgene bottle. So this morning I lay my backpack flat on my lap, ie my bottle was lying horizontally. Then dunno why I went and unscrew the bottle cover and... *splash*~
Luckily my Osprey backpack has the waterproof membrane.
(in industry, when they manufacture compressor, the product has to go through a leak test chamber to test for leakages. 100% leak test.)