Forzenny,
I agree with you on many counts. It is unlikely that anyone will want to carry much more than 2 gallons of water on their backs and that only at the expense of not carrying other needed supplies. Good filters are worth their cost and weight in backpacking scenarios. Chemical purification is adequate but again consumable.

OTOH, (you knew that was comming <img src="images/graemlins/wink.gif" alt="" />) I don't agree that you can't plan ahead and have 8 - 50 gallons of water on hand when an emergency strikes. In any building you might be in it is a simple matter to get a couple - many bottles of spring water and store them under a table or desk against a rainy day. I have 20 gallons in my basement and my office has two water bubblers that each have a supply of 20 - 5 gallon bottles lined up beside them each Monday. Friday there is always a few left. My car has two gallons in it as does my wifes.

Also I don't agree with the lack of utility of boiling in a survival situation. If you are lost and down travelling isn't always the way to go. If you are stationary it isn't at all difficult to keep a fire burning and for many reasons that is the best thing to do. fires provide signal, warmth and cheer as well as allowing boiling of water supplies, sterilization of medical and other cutlery and clothes (necessary for the women after a few days) and cooking of foods. Many survival situations will involve self-extrication and in those scenarios the filter or puri-tabs will shine. In scenarios with a more stationary "wait for rescue" flavor a continually burning fire is a welcome addition to the camp.

In the BOB / Evacuate scenarios - not all are on foot. Certainly if you are on foot there is a realistic limit to what water you can carry but even in those scenarios there is a limit to the water you need to carry. All you need to carry in an evacuation scenario is enough to travel quickly and as lightly as possible to the evacuation destination. (presuming enough planning to ensure that the destination has a supply closet with water in it. In such a scenario all you need to carry is a maximum of a gallon per person - immanently do-able - and the time taken to process water with chemicals, a filter, or boiling is too much of a slow down. In evacuation scenarios speed of travel is the primary concern. In a vehicular evacuation there is no serious limit to the water you can carry. 20 gallons fits in the trunk along with the bob and if you have a pick-up or jeep so much the easier. It is just a matter of planning to be able to load and go quickly enough and plan on packing the water as well as the firearm.

So the only time that the water carrying capacity is a real concern is in the long trail scenarios where you will be traveling by foot for long distances / times. This is a real concern for backpackers and hikers but not so much so for preparation to survive unexpected disruption of your plans by extreme circumstances.

Just my $0.02.