The primary problem is that the idea of "cleansing the colon" making the body "much more able to absorb nutrients from food" doesn't work because the colon doesn't do much nutrient absorption. Almost all the nutrients get absorbed in the small intestine.
There is also the problem that the body is constantly producing water in the digestive system, and most of the water we drink doesn't reach the colon anyway.
As a rule of thumb, though, any advice based on the premise that doing something "cleanses" something in the body is almost certainly nonsense, especially if they are vague about what exactly is being cleaned out and why it makes a difference. Your body is pretty good at cleansing itself, and if there is something it cannot get rid of you need a more serious intervention.
Edit: link changed to be from the NIH.