As long as you are happy with your climb rate then keep the water. The advantage in the cruise of flying heavy requires no skill or effort but achieving the advantage of lower wing loading in the climb does and it is easy to throw it away through lack of technique or lapse of concentration. As soon as you are unhappy with your climb rate, and don't expect better conditions ahead, then dump it bit by bit until you are. The happiness factor includes things other than theory or algorithm such as comparison with other gliders (if any), conditions ahead, current altitude, terrain below, pilot risk aversion level etc. Stuff that may not seem so important in simulation as in real life.