My first thought on reading this when Captain Stable posted it over on the Medical and Health forum was 'Uh oh, another urban myth'. The idea that 75% of Americans are chronically dehydrated is absurd.
This all feeds into people's already present anxieties and indeed the fear of dehydration and a dry throat are very common symptoms of generalised anxiety, whose prevalence has reached epidemic levels in our Western societies.
Drink as much as you need not to feel thirsty and to feel well. Don't count how much you drink or you'll become obsessed with it. There is no evidence that drinking more prevents diseases of any sort. The only time you probably want to force yourself to drink is in very hot climates when you're outside and then it can indeed be hard to keep up with fluid requirements (8-12 litres a day).
Otherwise, don't sweat it. (Pun intended.)
QDM
P.S.
I am reliably informed that a 70kg man needs 3 litres of liquid intake in 24 hours. This does not, of course, mean coffee, tea, coke, alcohol etc. as they are all diuretics.
This is true, but there's a significant amount of fluid in the food we eat, so it doesn't translate to 3 litres of drinking per day, unless you're not eating.