MAH from Blue Springs, MO on 9/22/2008 7:43:56 PM:
I believe it's Nov 1st and then back on April 1st. Just in case you're new to the trail, not all trailheads have running water at the trailhead itself. Starting from the western end, I know for sure that Clinton, Calhoun, Windsor, GreenRidge, Sedalia, Pilot Grove, Boonville, NewFranklin, Rocheport, McBaine, Hartsburg, and North Jefferson all do. Clifton City does not, so it's about a 20 mile stretch between Sedalia to Pilot Grove without water. I have read that if you go up the hill in Clifton city you can find a soda machine, but I have not done that.
Past Jeff City, I'm not 100% certain of the trailheads that have running water and which ones don't (although many times you can find a place to buy a cold drink if you venture off the trail.
Have fun!