One of the many skills acquired sectioning the AT is dealing with water. In order to get in the miles, keeping pack weight low is important and I think most folks are far better at getting the credit card out and buying super light weight gear than managing water. Even 25 years ago the AT maps and the AT data book gave a very good view ahead of water sources and current electronics databases are even more accurate. I started out carrying the entire days needed water but over the course of subsequent trips I figured out that there is no need if there is known reliable source ahead. I generally use chemical treatment, Aquamira, which does introduce a bit more challenge than a filter in that the chemicals generally need an hour (or more if the water is very cold) in order for the water to be treated. Thus I tend to have a reserve 500 ML Gatorade full bottle in the pack most of the time during the day. When backpacking I force myself to take a 5 minute break every hour even in the morning as I find it extends the overall hours I can hike in a day. I usually plan at least some of the breaks at water sources so I just keep the treatment handy and first thing I do is mix the components. The two components need to react for five minutes to get the telltale green color and chlorine dioxide odor and the last thing I do at the end of the break is add it to the bottles and head out. I also believe in drinking a lot of water before heading out of camp in the morning.
This method can sometimes be an issue down south especially in the summer and fall, unlike the AT in New England that tends to be somewhat perpendicular to the ridge lines where valleys are frequently crossed, much of the southern AT is ridge running for miles if not days. This is great for cranking out miles as the actually daily profile change can be quite minimal but not so good for water, as water generally flows down hill to the base of the ridgeline. Generally the water sources are in minor saddles in the ridge line and during a typical summer the primary water sources can and will be dry up high. In PA, there was a couple of shelters that had Water Source #1, Water Source ##2 and Water Source #3. They were all basically the same drainage, just at different elevations heading down the ridge with #3 usually several hundred feet vertical down slope. At more than a few shelters they warn hikers that the water source is way down the side of the mountain and that's where a large empty water bladder is of some value as you only really want to head down the slope once to fill up. Over 10 years of sectioning we really only had one trip where generally reliable water sources were dry and they were at shelters. In all cases we were within a hour of major stream or water body but dry camping in hot weather is not that pleasant. We knew water may be an issue on the trip and I brought my empty water bladder which consists of a ripstop nylon bag carrying a foil pouch saved from wine pouch. (It makes a nice pillow when not being used for water duty). In one case we stopped and filled up the bag up 3 miles before the shelter, the next night I spent a couple of hours pulling water out of mud seep because the normally reliable water sources at the shelter was totally dry and the last night my friend ended up digging the bottom of spring out about a foot deeper and dipping it out with cup. In all three cases, if we were desperate we could have put in few more miles and gotten to a more reliable source.
This actually can also be an issue in Maine, the original AT shelters and campsites tended to be in valleys, this may have been good for water but no so good as that meant they were usually close to roads and subject to a lot of car campers and fisherman both of whom could cause abuse and trash at the shelter. When the AT was substantially relocated in the 1980s due to the land claims settlement in addition to the NPS taking over the trail, the new shelters tended to be built up on the ridgeline nearer to the high point of the ridge and well away from more casual "drive in" users. Starting at Carlo and Full Goose in the Mahoosucs, there are several potentially dry shelters along the AT in western maine, Hall Mountain and Bemis both being somewhat notorious. There are very good water sources at the base of these potentially dry shelters and over the years informal and now formal sites have reappeared in the valleys on occasion. On my AT boundary section there is beautiful spot with picnic table near a wide stream in Sawyer Notch (no longer car accessible) and a new official campsite with composting privy has just appeared off South Arm road. This area has numerous bootleg sites adjacent to the stream and no sanitary facilities so I expect the club just decided controlled camping set back from the stream with a privy is better than the alternative.
I probably carry all the water I intend to consume about 60-70% of the time too but I've been doing more and more filtering the past few years. Can dramatically cut pack weight which helps me with my overall range and in Summer I tend to drink a ton of water when it is hot, far more than is practical to carry.
