This is definitely one area I slack on, I might drink 2 liters per day at best, however I'm never thirsty! It's an effort to get all that water in but I'm positive chronic dehydration can cause a variety of problems
Around 3 litres for me. I don't more than that is needed unless you are pretty active during the day and sweat quite a bit. Or if you are on tren or dnp lol