You can call the product waterproof, when it is made of material which resists at least 2 000 mm of the water column – that is what standart says. For the real outdoor challenging activities, you need more then that. In most cases, there is a real use of 15 000 mm water column and more. The water is being pressed into the product when doing outdoor activities (walking trought the grass, crashing the bushes, riding a bicycle...)
If you are into examples, when sitting there is a equivalent of 5000 mm, when kneeling down, 12 000 mm, even your backpack harness appeals on the product with an ammount of 18 000 mm. From this, you can easily say that the ideal product for outdoor activities should have at least 20 000 mm water column.