What do you think about this ending to a movie?

So I'm writing a movie script with my friend. I'm not gonna say what it's about, but there's this big war over drinking water. a lot of people die and there's a lot of hardships involved with the war and stuff. The thing is, we don't want it to be one of those "and they all lived happily ever after" movies. There has to be a twist or something. I was thinking that maybe the water that they find isn't drinkable for some reason. If you were watching this movie, would you be upset if the water wasn't drinkable and the war was all for nothing.