Does water become impure upon contact with a small amount of dry impurity (such as urine or wadī) on underwear, and does impurity thereby transfer to outerwear, which would negate the benefit of the ruling of pardon for a small amount of impurity?

Whoever is afflicted with obsessive doubt (waswasa) should not rule something as impure except with certain conviction. If the impurity of a specific spot on his clothes is confirmed, then by pouring water in a way that covers the impurity and drips from it, its purity is established if the impurity is

a ritual impurity like dry urine, and the water that covered it remains pure. If the water does not flow over the impurity but merely touches it and wets the spot, then it remains impure. There is a difference of opinion regarding the transfer of impurity from it to dry clothes, and the one afflicted with waswasa may adopt the view that it does not transfer. He may also adopt the easiest opinions regarding the slight amount of impurity that is overlooked.