What hormone is involved in the function of the collecting duct in the nephron to retain water?

Recall that the primary hormone involved in water retention is anti- DIURETIC- hormone (ADH). If your rember that diuretic means increased loosing water through urination then you will know that the function of ADH is to keep water in the body since it is ANTI-diuretic. I like to use the mnemonic of diuretic sounding like diarrhea which is watery stool and hence also water loss (although through a very different mechanism). Once you established that ADH is the hormone that helps your kidneys keep in water you need to realize that the water rentention that is dependent occurs in the collecting duct; everywhere it is dependent on osmotic gradients. In the collecting duct ADH places little channels called aquiporins which cause increased water retention.