A practical target is 35 ml per kg of body weight, plus about 500 ml for every hour of exercise. For a 70 kg adult who trains for an hour, that is roughly 3 litres.
Tea, coffee, buttermilk and the water in dal and vegetables all count. Very dark urine and afternoon headaches are more useful signals than any fixed number.
Drink a glass before each meal — it helps with portion control and is the easiest habit to build.