Anything that contains water (including vegetables and fruit
) counts. But sodas are junk to be avoided (esp coke - which - despite being a dring - has diurectic characteristic).
The rule is to drink often, and more then less. While I'd say that 2 gals/day is a bit excessive, 1-1.5 is usually enough.
However - I know people who could go through as much as 4-5 gallons during hot days (one guy is a pro cyclist, other a runner).
However - if during the day you feel thirsty, then you drank - TOO LITTLE - no matter how much was it.