I decided to research the medical effects of Cole sitting in the pond, and if it really helps.
I found that there is a whole field dedicated to dealing with different water temperatures and their effect on the human body. It is called Hydrotherapy. (1) It deals with the benefits of different temperature water and how it can be used treat many illnesses, some being arthritis, ankylosing spondylitis, and partial paralysis. Cole, in the book, uses the pond as a place to relax, and I found that the effects of cool water seems to support what occurred. When you enter cool water the body undergoes a process, that process being; the initial shock of the cool water (but upon repeated immersions the body gets used to this), then the body quickly begins to react. The feeling of cool is replaced with warmth and a feeling of exhilaration as the pulse quickens; the respiration becomes easy. However, if subjected to the water too long, the water starts to feel cold again, and then the body starts to go downhill. Cole, seems to have experienced the body reaction to the cold water, but would leave the pond before the onset of cold began. However, in the book it mentioned that Cole's joint pains would disappear after the pond, but that relief is said to occur after immersion in warm water.
Works Cited
"Effects of Cold Water." Chest of Books. 5 June 2008. 8 July 2008
"Hydrotherapy." Wikipedia. 7 July 2008. Wikimedia. 8 July 2008
"Responses in Subjects Immersed in Cold Water." Journal of Applied Physiology. 8 July 2008