Wrong method! You cannot just slowly go in cold water. You need to go in all at once! Less agonizing. It is also all relative. Go in cold water, all at once. Get out. Wind on wet naked body makes you REALLY cold. Jump back in water - it actually feels warm. Another trick - take your bath mid-day at a rest break. Usually warmer and you quickly warm up again. You have not lived until you have taken a snow bath. That is what high altitude climbers do.