I started this with a goal of one month. But when the month was over, warm showers just didn't feel right anymore. Definitely added willpower XP and remedied my dry skin.

http://impossiblehq.com/cold-shower-therapy-guide

http://www.artofmanliness.com/2010/01/18/the-james-bond-shower-a-shot-of-cold-water-for-health-and-vitality/