Still one question arises: why the use of running cold water (not mind-challenging towering waterfall of the Japanese kind) has not been covered much (if at all) in traditional Buddhist or Taoist practice literature? The reason, I believe, is that taking cold shower has been the norm rather than the exception in those days. For a practitioner of chi-related discipline, a simple advice of NOT to take hot water bath will be sufficient for a good training guide. And that is exactly what had been taught in Taoist meditation Neidan: Doing cold bath/shower can nurture one's golden pill (金丹), whereas doing hot bath/ shower will lead to losing one's hard-earned golden pill (走丹).
Such cursory training mention is definitely not sufficient as good training guide for the modern man. And the huge benefit for taking cold shower deserves the good attention of all modern practitioners seeking for a better chi-energy.
The next question: what is your advice for practitioners who want to open their chakras? It is the reason of existence of this little article.
As with everything worth-trying, the method is simple, assuming some foundation training (after all taking cold shower for chi generation is an advanced practice). The first required foundation is some good training in zhan zhuang (standing meditation) or seated meditation, so that one can use his stretched hands to guide his chi movement. The second required foundation is the ability to point focus on one's crown chakra (頂輪), one's heart chakra (心輪) and one's root (or perineum) chakra (海底輪).
After one is "warmed up" with cold showing one's body (i.e. one can relax rather than shiver under the cold showing), one can run the cold water down directly toward one's crown. Maintaining a relaxed and non-shivering body, one focuses on the central channel (nadi) or zhong mai 中脈, that joins all the chakras. Join the chakras with a focused mind. Criterion of success: you will feel a new sensation of quiet existence, without any feeling of being cold. Enjoy!