You don't need to start right off with a 2kg pack. You want about .5L of water per hour hiking. Throw in an extra bottle perhaps, better to have a little extra

You don't need to start right off with a 2kg pack. You want about .5L of water per hour hiking. Throw in an extra bottle perhaps, better to have a little extra than not enough. 2kg of water is about 4 hours hiking. Maybe don't start right off with such a long hike.