One of the most important things to think about when you are hiking – and even more on a backpacking trip – is water. On short day hikes it isn’t as important as multi-day trips, although you should always bring SOME water with you in case you end up out there longer than you planned.
But on a backpacking trip you need to think more carefully about your water, you can obviously only carry so much with you and the weight of your pack can be the difference between a wonderful time and a real drag. So the weight of your water container as well as the water itself can be a factor. Each liter of water weighs about 2 pounds. You will also need to replenish your water, and will need to plan for some kind of water purification.
This video was done by a veteran Appalachian Trail hiker, and in it he shares his preferences for water containers and why he chooses them. He also points out in his notes on YouTube that the SmartWater bottles do not contain BPA, they are made of type 1 plastic (actually most soft drink, water, and sports drink bottles are made of this type of plastic, but if you are in doubt check the number on the bottle!). He points out you may not just want to have drinking water with you, but you may also need some way to store water that you can filter later – the streams don’t always show up at the most convenient time!
He mentions the Sawyer Squeeze filter system as something that he uses in his pack. These filtering devices are very small and easy to use, and the manufacturer claims that it will last a decade without needing to be replaced. The design is something that came from kidney dialysis, and is made to work 100% of the time (according to the manufacturer).
Everyone loses water at a different rate, so you will need to pay attention to the amount of water you drink to stay feeling well. Many people bring 2-3 liters of water with them, but if you know you will encounter water sources regularly, you can probably do OK with the 2 bottles that are recommended in the video.