That water was poisoned for sure. Though if you filtered and boiled the water, it might be drinkable. Totally mind boggling that you would risk Glenn's life for something that wasn't needed. Still not as bad as stopping in the middle of a freeway graveyard and getting surprise attacked by a pack of walkers.
It's like they want to die.
"And so he spoke, and so he spoke, that lord of Castamere. But now the rains weep o'er his hall, with no one there to hear." - The Rains of Castamere