Water containers come in many sizes and styles so you need to choose the most appropriate water bottle or water bladder for the adventure you are undertaking. Here's a quick Nomad run down:
*5 lt - 1.5lt standard water bottles - individual use
*1 lt - 2 lt collapsible bladder bottles - individual use
*Water chambers - individual use for inserting into a compartment in your rucksack or daysack with a straw
*5 - 10 lt bladders - designed for camp use
*Flasks - for individuals to keep drinks warm/cold
For individauls it is best to carry two litres of drinking water on you at all times. This can be in one large container or split between two smaller containers. For those on a high exertion expedition or trek, you will need to carry upto 10 litres for the day.