Hydration is basic stuff to anyone leaving home. The older way is to carry a water bottle, but nowadays you have a choice between a bottle and a very handy water reservoir.

The water bottle

A basic canteen is easy to pack, use, and clean. Usually takes around 1 liter / quart of water. We got both army surplus canteens and new canteens and water bottles.

A good companion to a drinking bladder because it's much easier to pour out water from a bottle than from a bladder.

Hydration pack

Ahh, the modern way of drinking on the move is of course the hydration pack. Although water containers carried on the back are an age-old invention, at some point someone decided to add a tube to it so the water could be drank directly from the reservoir.

The hydration pack and hydration bladder are kinda two different things; the pack usually means the combination of a bladder and its carrying pack or the pack only. The bladder means the reservoir itself.