There’s a difference between the three of them.
Let’s compare their dictionary definitions to their company and advertising definitions.
water-resistant: designed to not be easily harmed or affected by water or to not allow water to pass through easily
water-repellent: treated with a finish that is resistant but not impervious to penetration by water
waterproof: (1) designed to prevent water from entering or passing through; (2) designed so that water alone will not remove it
This is the lowest level of water protection of the three. Anything that’s labeled “water-resistant” is either designed in a way that makes it difficult for water to penetrate it or is coated with a light substance that improves its chances of surviving its contact with water. It has the power to withstand the average hand-washing or light rain shower.
This is supposedly a step-up from “water-resistant”, but that’s debatable. Anything that’s labeled “water-repellent” is usually (not always) coated with some form of nanotechnology (inside, outside, and/or both). It has the power to withstand liquids such as rain, mud, ketchup, and syrup.
You may think this is the best among the three because it conveys the idea of “total protection from water”. However, there’s no established industry standard in order for something to be labeled as “waterproof”. Anything that’s labeled “waterproof” usually (not always) means that it can be submerged. How “waterproof” items are protected from liquids; how deep they can be submerged; how long they can be submerged; and what kinds of liquids they can be protected from varies.