If you go to where you got the cleansing water, and fill up the WtrJr again, then the WtrJr will turn into theWtrJr'. The WtrJr' contains the cleansing water, which, when used in battle, will restore a ALL HP and AP to the party members. This can only be used ONCE, before you have to go refill the WtrJr again. You can refill the WtrJr as many times as you want. Note that trying to fill it up more than once in a row, won't affect the number of times you can use it after that. No matter how many times you fill it, you can only use it ONCE, before you have to go refill it again.