He asks celebrity participants on the show, including sports presenter Gabby Logan and singer Alfie Boe, to have a cold water shower of 12°C every day, increasing the duration of the shower over time from 15 seconds to two minutes.  Watching the reaction of the participants under the cold shower shows you that it is not a pleasant experience, at least at first. 

There is not much research looking at the health benefits of cold showers, so the literature is limited. The largest study with 3,000 participants was carried out in the Netherlands and found that people who took a daily cold shower (following a warm shower) of either 30 seconds, 60 seconds or 90 seconds for one month were off work with self-reported sickness 29% less than those who had a warm shower only. Interestingly, the duration of the cold water did not affect the sickness absence.