Water weighs in at  8.34 pounds per US Gallon or by the litre its .7 kg or 1.6 pounds, and humans need on average of 2.2 - 3 litres of water per day.
When we are packing for a motorcycle adventure, water and fuel are often left to the end to be fitted into whatever space remains, but considering the weight and bulk of liquids, not to mention the challenge of leakproof containers, perhaps it should be our first consideration.