Two notes to add: First, let the crap settle out. Pre-filters and flushing are fine, but the best idea for really contaminated water is to put it in a bottle, and let the big chunks settle. Carry a transparent/translucent Nalegene (or something, a gatorade bottle...) for this if needed, and don't forget it's a contaminated bottle even when empty. Let the dirt settle (even 10 minutes is usually pretty good), pour off the clean to another one (carefully) or use the filter hose carefully. Extends the life of filters a lot.
Second, get the right tablets! There are two types or tablets available on the market and in the supply chain. Iodine and chlorine dioxide. U.S. military or commercial iodine tablets are suitable for purification of bacteria and viruses but have no effect on Cryptosporidium and a low to moderate effect on Giardia so are not something I even permit people to carry for purification.
Chlorine dioxide tablets are suitable for bacteria, viruses and has a low to moderate (slow) effect on Cryptosporidium and is highly effective on Giardia. You're most likely to find Katadyn Micropur Purification Tablets available in the US. Aquamira tablets are NSN 6850-01-551-7850.
Chlorine dioxide tablets come in individual foil blister packets and have a shelf life of 4 years. Do not use old tablets! Also, none of that taste worry with iodine so use them.
- If you suspect the area you are in (proximity to livestock) has Cryptosporidium contact time is 30 minutes for clear water, 4 hours for turbid water.
- Remember that the colder/dirtier your water the longer any purification tablet will take to work. It won't become re-contaminated if you wait longer, so just wait longer if not sure, plan for purification before rest cycles so it's ready when you get up.
And actually last: Read the instructions and follow them carefully. Practice and make sure everyone understands procedures. It's easy to mess up which hose or bottle has been where and contaminate your drinking water, or to do things like forget to flush the threads.