That depends on the type of boot. Boots with a waterproof lining should stay waterproof through the life of the boot. Boots that use a weatherproof spray or treatment on the outer part of the boot usually need to be reatreated about once a month with the waterproof spray to ensure they remain waterproof. Waterproof boots with full-grain leather construction and welted seams will stay watertight longer than those with lower quality materials, such as top grain leather and cement seams.