Most minimume 2 liters - Almost daily 4 liters - When I ride winter 1 ltier every 18 miles (29 Km) - 100 degree + weather about 1 L per 10 miles - I also have one hell of time ballancing my electrolites but I am 57 and about 230# - Younger athletic guys do not need as much water as I do...
During the summer time here in Texas I have to change my bike routes to accommodate my water needs...
I have wished for a zipper on my spandex... Oh Well...