We suggest you have one liter in the morning, before you start trekking.
We recommend drinking 4-5 liters a day. We suggest you have one liter in the morning, before you start trekking. Then, fill your bladder with two liters of water to drink on the trek, until lunch time.  Finally, at lunch, you can refill the bladder with another two liters of water to drink for the rest of the day.  If you can follow this routine, you will avoid headaches and overall fatigue from dehydration.