Something interesting that I found out recently is that in addition to everything else that has been said here water is also important because it can help prevent diseases later in life. It does this by flushing the toxins out of the body. Think about this--If you eat food that are unhealthy for your body for an extended period of time, and you rarely drink water then those toxins will sit in the body and eventually have a negative impact. I truly believe that water can help all sorts of health ailments in addition to nourishing the hair.
