I've never drunk much water, except when in a hot climate when I can drink liters! I drink enough liquid to satisfy my thirst - 2 or 3 cups of coffee during the morning, a cup of tea after lunch, glass of wine with dinner and that's usually all for the day. OH is the same, except when on treatment for prostate cancer when he had to drink a lot of water before radiation therapy. One daughter always has a water bottle with her and blames all ills on not enough hydration.
Sister in law visited recently and drinks even less! She doesn't drink tea or coffee, hardly any plain water - prefers the fizzy sort, and not much of that. She's 65, has excellent skin and health - we were looking for the "senior" rate when visiting an attraction and she was asked for ID to prove her age. (OH and I weren't asked, but both over 70).
I think the constant water drinking is a fad - there may be times when you need more but mostly drinking to satisfy thirst is enough. Friend's mother never drank much - hated the taste of water but lived to her late 90s.