The minimum amount of water you need depends on our body weight. As a general guide, for two pounds of body weight, an ounce of water is required. This means, approximately, for every 1kg of body weight, you would need 0.033 litre of water.
"Water (in litre) to drink a day = Your Weight (in kg) Multiply by 0.033"
So, if you are 60kg, you should drink about 2 litres of water every day. And for 90kg weight, you'll need about 3 litres of water. All you need to do is multiply 0.033 to your weight in kg.