Modern waterworks plan for about 200gal/capita day, although tactical infantry operations might plan for 5 gal/manday.
Roman aqueducts serving Rome also provided about 200gal/capita day or about 1 cubic meter of water per person/day.
Thanks. It’s all very well to talk about water supplies, but quantities are at the center of the issue.
When I used to go backpacking in the desert, we planned for a gallon per day. Which sometimes got kind of thin.