The calculation refers to the minimum physical activity during the day (1/2 hour walk).

ManWoman , body weight 5051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100101102103104105106107108109110111112113114115116117118119120121122123124125126127128129130131132133134135136137138139140141142143144145146147148149150 kg, needed during the day 1.75 liters of water (that's 8 cups to 2 dcl).

Note that about 30% of the liquid requirements (in your case, the 2 glasses) are taken up by food.