You can find the value of water column in the description of the product. The water column indicates how waterproof the fabric is. The higher the value of the water column the more water pressure a jacket can withstand before it soaks through. Waterproof ratings are measured at laboratories: a column of water with a diameter of 2.5 cm is placed on top of a fabric and the level at which the water begins to seep through is recorded. The results are measured in mm; as such a 5,000mm rating means that the water has permeated through the fabric at the 5,000mm level so it is not as waterproof as a fabric with a 10,000mm resistance.
A standard waterproof rating is about 5,000mm , but in general this will only be rainproof and not waterproof. Watch the video.