For a healthy person if they have choice between dehydration and potentially catching some sort of side effect from contaminated water, the choice is easy, drink the water and take a very slim chance on getting a water borne illness in few days. The potential pathogens are pretty minimal as the water source is basically rainfall and dew condensing on the summit then running down through shallow soil to the well. Sure, there can be occasional contamination from poor sanitation, but a healthy person can usually tolerate it. There are much referenced studies that tests of hiker's water bottles being brought into backcountry areas have a higher level of contamination compared to the water being carried out. Over the years I have encountered many under equipped dehydrated hikers in the whites on a hot day asking where the next water is. I usually tell them where the next water is and do not go into water treatment as I know that the odds of them having dehydration effects during the hike is far higher than a possible side effect from contaminated water a few days later.
Palatability is a different story, talk to any PCT thruhiker about water quality and most will admit that the quality of water they would drink went way down compared to East Coast hiking during the initial desert section. Many water treatments can kill all the nasties in the water if the directions are followed but the resulting water still may taste bad. I have drawn water from sketchy sources in the past and treated them with a chlorine dioxide based product to make them safe, but the water still had a significant taste.
Anyone who used to use polapure no doubt remembered the poor palatability of any water treated with it. It made the water safe but it definitely had a big tradeoff.
Given that a UV pen, life straw or aquamira all weigh very little, its easy insurance. I do have a lot of issues with hydration and its reinforced to me post hike via leg cramps that I should be stopping and drinking more. Electrolyte tabs can help but no substitute for drinking enough over the course of a hike.
Note Crytosporidium which is carried by livestock can multiply rapidly enough to impact a hiker on his/her extended trip in some cases less than 48 hours. Its not really an issue in the backcountry but can be one in areas with livestock.