Summary and maybe clarification:
1. know the trail. Use guidebooks (I like The Thruhiker's Companion, ATC) for general water availability on any particular day's walk, but springs and rills go dry late in the summer, so get up-to-date info from hikers you meet as well as Whiteblaze. Thruhikers have a spooky grapevine, and can usually tell you if the next 10-15 miles has water or not, even if they have not been there yet themselves. That said, you will probably pass more than one water source during the day. Just make sure you stock up in anticipation of need.

2. Your water demand during the day is something you have to learn. A good idea is to drink your fill (more than you think) before leaving camp, then plan on using at least two liters during the day. Dehydration drains energy as fast as starving and lots of hikers don't drink enough. The rule is: By the time you are thirsty, you are already dehydrated. Drink early and often.

3. Your water demand at camp is also something you have to learn. Desert adapted wilderlings make every drop count, but that involves learned skills. Most folks waste lots of water. If you plan to make a dry camp, you really ought consider having at least 3 to 4 liters if you plan to cook 2 meals. Remember, you will also need enough water to last until you reach a source on the next day.

4. Plan ahead. A dry camp is no problem if you can tank up a few miles before you camp and can walk to the next water source the next day before you run short.

5. Consider alternative strategies. Shelters are often near the only available water. Some wilderlings (your's truly included) don't like to camp in or near shelters. I like stop at a shelter to cook supper (and socialize), tank up on water, hike 3-5 miles in the evening, and then hike to the next water to make breakfast in the morning. When I can do that, I dry camp with, usually, 2 liters. I'll polish one off in the night, and drink the other down in the morning.

6. Rehydration mixes restore electrolytes and make your water go farther. I prefer artificially sweetened ones because I hike better on complex carbs instead of the sugar found in most mixes. My favorite hydration mix is not sweet at all: unsweetened lemon Koolaid mix, table salt and salt substitute (for potasium). A swig of that perks me right up.