Correct, the VANN drinking bottle is indeed 100% leak-proof with the carrying cap and the pouring cap. Our advice is not to use the cap with straw when you put the bottle in your bag, as this can lead to leakage. This is with the emphasis on can, because the cap with straw does not leak easily. However, when another object in your bag hits it, the cap may start to move. It is our priority to prevent a wet bag, hence this advice.