Rather than aiming for intake of 2litres per day, I prefer to ensure I produce 30ml urine per hour - approx 750ml per 24 hrs. If I assume 250ml = "a decent pee", then 3 decent pees a day means I'm drinking enough, as that accounts for other fluid loss through sweat, expired air, faeces etc. An extra check on colour of urine shows I'm not dehydrated nor have missed hyperglycaemia (should be pale straw colour; too dark means dehydrated; too pale means hyperglycaemia), but is much easier in a white porcelain toilet than when peeing behind a tree, for example, as I often do when adventure racing (races over hours, not just minutes) etc.