Re-reading this long thread, James Mattis' post really struck home. Clean, potable water would be a top priority.
You are probably familiar with the myriad of devices from straws to cannisters and pumps, for purifying water. Most all of these work well.
There is a simpler technique, however, Betadine (tm) SOLUTION (NOT SCRUB; the scrub has soap in it) is available over the counter, and is a good wound cleanser (dilute to 1 part Betadine (tm) in 10 parts clean water).
You put 10 drops of Betadine (tm) SOLUTION in one liter of water. This kills bacteria, viruses, amoebas, and Giardia. It is widely used outside the US for water purification, but the manufacturer is not interested in selling small amounts for this purpose in the USA. It is easier than carrying around the Iodine crystals, and doubles as a wound disinfectant.
Dr. Walt says, post-Apocalyptic dysentary is NOT FUN!! Walt