Running down the list in my head of the total liquid consumed in a typical day (excluding hygiene needs, just what I drank):

1.0 liter pre breakfast water
.75 liter breakfast (2 ea 375 ml servings)
.5 liter morning coffee (2 ea 250 ml servings)
.75 liter lunch (2 ea 375 ml servings)
1.0 liter afternoon tea (2 ea 375 ml servings)
.75 liter dinner (2 ea 375 ml servings)
1 liter evening refreshment

For a total of about 5.75 liters, or 1.5 gallons per day under moderate activity. Any exertion beyond normal, such as a trip to the jobsite or relocating my hooch, and you can easily add 2 liters or more to that level.

In a hot, dry environment under normal exertion, 2 gallons direct consumption would be the minimum.

Even here in Brisbane working in an office, I likely consume at least a gallon a day, though admittedly some of that is non-essential (the trip to the pub with the crew accounts for a liter a day 3 times a week) <img src="/images/graemlins/smirk.gif" alt="" />

It is looking more and more like Reverse Osmosis systems are coming of age finally. Globally RO manufacturing cannot keep up with demand, and there's no other suitable technology for desalinating or recycling water. Given the amount the Middle East is investing in Desalination plants, as well as other places such as New York City and here in Australia, where the drought has just been upgraded to a 1:1000 year cycle (meaning it is dangerously low), I can foresee the need for individual water treatment systems becoming a viable option soon.

Hard to imagine, but even Antarctica appears to be in the midst of a major drought!

I can foresee that instead of drilling wells, people will have atmospheric condensors pulling moisture out of the air to supply their households. Technology marches on I suppose.