Well, Most of the southern AT you can resupply every 4 to 5 days and do so fairly easily. So you could drop 2 days of food out of the pack. many people hike to within say 4 or 5 miles of a town and camp. Get up and hike in for breakfast (so you didn't have to carry that one). If you are up at 6, hiking at 7 and hike 2 MPH, you are still ordering breakfast at 9 AM. Be recharging electronics while eating. Head over to what ever store is around for resupply. Many folks then walk to the hostel or other place to recharge their electronics while paying $4 or 5 for a shower and cleaning clothes. Have lunch. Hike out of town with a sub sandwich in the pack around 3 or 4 in the after noon. "Nero" as in you hiked a few miles in the morning and a few out of town.
Water. Download the Far Out app. Download the free approach trail of the AT just to get used to the app. Watch some How-To YouTubes on the app. They should have a sale on the actual trail coming up around November and December. So then purchase it and download it and the way points and whatever else looks interesting. That way they are available when you don't have a cell signal. Look at all the water you can find. Notice that people post on the App about the "Seasonal" water that is noted in the App and also on like the AWOL guide. That way you have some idea of what water is ahead of you. When you reach a water source, be down to your last cup. Camel up while at the source. Then practice what you really need to carry. I think most people carry a bottle or two (1.5 liters perhaps).
Water and food weight is what many people carry too much of. The old "packing your fears". And yeah I still do it. Usually a package of pop tarts or two granola bars are still in my bag when I'm back at the trailhead, my truck or wherever I have more food.

I rarely talk about pack weight or gear as my thru was in a different time and thus not relevant today but I'll give you my experience.

You'll never need 5 quarts of water. I actually only carried 1 quart from Springer to Damascus, where I added another quart water bottle. (I would never recommend that anyone start out with just a quart). 2 quarts was all I needed, although when you get to NY if it is a dry year you may find that adding another another quart makes sense. If that happens just buy a Gatorade and keep the container as long as you need it.

I weighed my pack the night before I left and it was 52 pounds. I decided that anything over 50 pounds was ridiculous so I got rid of 2 pounds. By the time I got to Damascus I lowered my pack weight from 50 to 45 pounds fully loaded which is where it stayed (with one exception) the rest of the way. That 45 pounds included about 10 pounds of food so I was around 35 pounds as I entered town. The exception -- I entered the 100 mile wilderness with 10 days of food, a rotisserie chicken, and an adult beverage. I also bought a heavy shirt in town as it was starting to get cold. If the scale at the hostel was accurate my pack weight was 62 pounds. I noticed the difference so I believe it was accurate. Didn't need all that food as I finished the section in 6 days.

Keep in mind there are plenty of opportunites along the way to either buy additional gear or send gear home. Mountain Crossings at Neels Gap (mile 30) has a great reputation for going through hikers packs and making suggestions. The amount of gear that UPS picks up there every year that is returned to the hikers home is astounding.

So...can you carry 43 pounds when you leave town? Absolutely. But there's no reason to do so and I would encourage you to take a look at your gear and see if there are a few things you can do without. You can start off by losing about 6 pounds of water. Lighter is really better all things being equal.

BTW, I have no idea what my pack weighs these days as I haven't weighed it in about 20 years. I take what I need -- and what I want -- and everything seems to work out. I do know that I'm lighter now than back then. Still heavier than average.

I love trail towns. I love clean clothes, hot showers, and town food. I prefered a town stop every 5 days -- of course you don't always get what you want as it depends on your pace and the location of the towns.

First, welcome to the Cafe Packrat.
Water weighs 8 pounds a gallon. At 10 pounds that means you'll be carrying over a gallon. Not o ly is that heavy but it'll take up a good bit of room in your pack. Like someone else suggested, carrying 2 quarts should be enough.
Feel free to ask any and all the questions you have.
It's a very friendly bunch that hangs out here.

Another thought and why people look to shed pounds and then ounces. It all adds up. On your back, your hips, your knees your ankles and finally your feet. The more weight also means you probably will hike slower. So your miles drop down. So you have to carry more meals. It becomes a Catch-22.
Last time I hiked and weighed the pack, fully loaded with two Smart water bottles. I was hiking a place with water everywhere. I carried three days of food (which was about half a day more than I thought I'd need) and was at 25 pounds pack weight. with some items I could drop. Like a Leatherman when I had my Benchmark knife anyway. Like some extra hammock suspension stuff that I wanted to try out for a day. Like a backup battery bank. Which actually came in handy because it has a small light on it and my headlight got upset with me, failing to work at night but magically working at first light (go figure). But all that extra stuff was probably half a pound.

Welcome Packrat!

I'm similar to you in anxiety about running low on water. I suspect that you'll do some training between now and 2025; perhaps you could hike some AT sections or similar trails and see how you do, water-wise. Much (then, or in 2025) will depend on any drought conditions.

Sometimes, even in a drought, there are water seepage sources to be found, but you have to know where to look, and you may have to have a pump-style filter because it's not likely going to be dripping off a rock or running down a creekbed. Possibly not even deep enough for scooping - thus the pump. See TipI Walter's trail journals on hiking in the furnace of WNC during the peak temps of summer. Hopefully, though, you'll have ample water supplies and be able to drop substantial water weight. From what I read, I don't think many people on the AT carry more than 2L at a time. You could, in fact, "camel up" at a source (say, drink half a liter, or a bit more) and then treat/pack your 2L. Then you'd be good for awhile.

7 days is a heavy cary & not needed on the AT. There are plenty of plsces on or close to th trail to resuppy without slowing down your hike much. Join ALDHA & you membership includes a PDF copy of their Companion guidebook.
aaon most section of ther trail 2 liters of water is the most you really need to carry one is more the norm. You will learn quick once you hit the trail so don't worry abou it to much.

When my husband and I hiked from PenMar to Harpers Ferry last June we were very deliberate about our food weight. We were hiking with a 75 year old friend, and wanted to be able to carry some of her items in addition to ours if needed. That being said, as we hiked in to Harpers Ferry we had eaten all but one granola bar. It was confirming to us that we could make a good food plan. Our friend, whom we have section hiked with since 2011, was amazing, strong and determined, and we didn't need to carry anything for her after all. What an amazing trip it was. The Maryland shelters, and the Dahlgren Backpackers Campground were fabulous.