I have set up a spread sheet. I aim to carry 1 gal/day. Shorter trips can get by w/ a little less water. For example, on a 3-day trip, often the first and last day are only about 1/2 days, so you can almost get by w/ 2 or 2.5 gal of water for the trip. Longer trips, like 7-8 days, you must carry 1 gal/day/person, especially if the days are warm. It doesn't happen often, but, people do have accidents and lose a gal or 2 of water. If everyone is carrying 1 gal/day/person, the loss of a couple gal by one person can be made up by the group.
Still, everyone has to be responsible and avoid water-loss accidents. It hasn't happened often in my experience.
Here is my spreadsheet for my upcoming trip on Feb 8.

Using the spreadsheet at my computer, I simply fill in the units column and make adjustments until my total is a gal/day. I count alcoholic beverages the same as water--it is close enough, as long as you don't overdo the alcoholic beverages. My wife has a similar sheet, but she will substitute Arizona Green Tea for some of my Gatorade.
As you can see, I use a mix of containers. Heavy duty Dromedary bags are the greatest--tough, non-leak containers, and they are malleable enough to stick just about anywhere.
One last comment for people from fresh water enviroments. If you are traveling in a salt-water, wilderness environment, there is NO FRESH WATER--water filters WILL NOT WORK. You must carry all your water. In South Florida, you can go a week or 2 w/ little or no food. You can last only a couple days without water. That truth is reaffirmed every year in this area with deadly results.
Keith