Help in selection of pack

[West Texan]

I am new to backpack camping and am going out for a couple of days in an area where I will have to carry all water needed. There will not be any water source on the trail. I am figuring two gallons of water for 48 hours and am having trouble finding out how to carry that amount of water as well as what size pack for this. Thanks in advance for any help.
WT