I'm with both of you. After drinking "city water" which has a chlorine taste, I love drinking fresh mountain spring water.
But the OP's wife does not. Some people don't like plain water. To each their own. HYOH. Unfortunately I don't have much to add except that the lightweight flavor enhancers or powdered drink mixes likely have artificial sweeteners in them. The heavy ones probably have real sugar. If this is important to the OP's wife, choose accordingly. If not, go by flavor... and since she's the picky eater (drinker in this case) why are WE trying to determine what she should drink? Have her experiment now - off the trail - to see what she likes and doesn't like; having her be mindful of the weight and bulk of the items she tries.