Just did a nice trip with 11 new backpackers on the AT - 19 miles from Washington Monument SP sobo to Harpers Ferry. Thought I'd share info on water and shelter for that section of the trail.
Wash Monument has a hose faucet behind the bathrooms at the bottom of the hill right before you leave the park. Dahlgren's campground has water. Gathland has a hand pump in front of bathrooms The springs are running well at Rocky Run and Ed Garvey shelters, but the hike down and up from Ed Garvey is ridiculous!
There were 4 hangers in our group and we had no problems finding trees, but the poison ivy is out of control! I would find a great spot, but then look carefully and see the stuff either on the ground or climbing up the tree
Leaves are starting to turn and fall, so you should have quite a hike in!