With a filter, you carry water to the next reliable source — not for the whole day. Enter the stretch ahead and get litres and pounds, with the reasoning shown.
Start with
2.75 L (6.1 lb)
About 3.5 h of walking to the next source. Includes a 20% buffer.
If the next source might be dry, plan to the one after it — a source you have not confirmed this season is not a source. Carrying a filter means you only need water to the next reliable source, not for the whole day.
Lighter ways to treat water: the best backpacking water filters. Plan fuel too: fuel calculator.
Only enough to reach the next reliable source plus a buffer — typically ½–1 L per hour of walking depending on heat, plus about 2.5 L if you will camp without water.
Around 0.4 L an hour in cool weather and 0.6 L when warm; the National Park Service advises ½ to 1 litre an hour when hiking in heat.
One litre weighs 1 kg (2.2 lb). Three litres is over 6.5 lb — often the heaviest single thing in a pack, which is why carrying only what you need matters.
Planning fuel as well? Fuel calculator. Building your list? Pack builder · The Shakedown.