Question: how much water should a 45 kg person drink?
Answer: Water (in litres) to drink a day = Your Weight (in Kg) multiplied by 0.033. For example, if you are 60kg, you should drink about 2 litres of water every single day. At 90kg, you'll around about 3 litres of water. All you need to do is multiply 0.033 to your weight in Kg.