I had to keep a fluid list when I had kidney gravel, but not for diabetes.
1.2litres in my opinion is a very low fluid intake and I drink approx 3 to 3.5 litres in 24hrs and that is not taking into account that used in cooking all the veg or within the fruit I eat.
Plenty of fluid is essential for your body to work efficiently and the link below will put it better than I ever could without C&P'ing the whole article
Ok, just wondered cos 1200ml doesn't sound like much. Also you said you were always thirsty, which sounds like maybe you're not drinking enough. Could be the diuretics making you thirsty though. Hope they sort it out soon