Use the resources available to you; guidebooks, apps, water reports, maps etc., and make an informed decision as to your requirements.

I always take a minimum capacity of 3 quarts and increase that as the hike dictates. How much I actually carry is dictated from the above data sources and what I am trying to accomplish on any given day. Longer mileage days I carry more so as to minimize the breaks. Although I can't, as a rule, cover the distance per quart that Garlic does, I have learned that it isn't difficult to get 6 - 7 miles per quart even in hotter desert environments. Over the last several years I have been experimenting with a drinking regimen whereby I drink a given amount of "sips" at set time intervals and have found that this works really well for me. I augment this by leaving water sources mostly hydrated having tanked up by drinking up to a quart of water. My test environments have been southern sections of the PCT, Big Bend NP epic hikes (twice), and NM/WY portions of the CDT.

As an aside I almost always dry camp. I think this comes easy for me as my body doesn't seem to require many fluids once I stop moving. At least I don't experience thirst. It isn't uncommon for me, aside from meal requirements, to drink less than 8 - 12 oz after establishing camp. Perhaps this is an indication that my hydration strategy during the day is effective...

The point of all this is to learn your body and what works for you specifically. It is, however, my observation that most carry way more water than necessary.