The term waterproof is used interchangeably with "water-resistant" and means that moisture can be kept from penetrating. However, the term waterproof or water-resistant never guarantees complete protection against
Thus, the term differs from "waterproofness," which means that under specified conditions, no water can penetrate. For example, a waterproof closure box can keep the items inside dry, even if the box is fully submerged in water. A water-resistant box, on the other hand, would only be able to keep out a certain amount of water or splash moisture.
To make leather bags waterproof, the material can be impregnated. More information on this topic can be found under the keyword "impregnation."
Source: https://ousuca.com/wasserdicht-wasserfest-unterschied/, Status: 31.05.2018
