it may be harmful beacause when you drink water while you are standing the water go across the stomach and it goes directly to the intestine and the water may have some bacteria so the stomach can't kill the bacterias.you may got disease but it's a small chance. I advice you to dring while you are sitting.
Yeah it is harmfull it is too much harmfull from which. Most important is the joints donot get sufficient liquid
if ur question is that any problem with drinking water in standing position.. and it will be problematic off course it is because of one. that on standing postion the direct mechanical force on throat that is on epiglatis and it is mainly by the gravity act. and other that on standing position water will directly passes through the stomach as usually but without any delay in stomach which will happen during sleeping or on other positions which make the foreign particles in water escape from the action of gastric juices .