We carry two one-litre water bottles. It is always tricky to decide how many of them to fill up in the morning. It is a matter of judging how long it will be before we can replenish them.
Whilst it is annoying to have water left over at the end of a walk, it is far worse to have to trudge the last few kilometres with your tongue stuck to the roof of your mouth. We never set off with less than a litre of water.
It is worth remembering that any bar will happily refill your water bottles and will sometimes even offer to add “sirop”.
The other reliable source of water is graveyards, which always have a tap for people to water their flowers with.