5ltrs is way too high an estimate. I would actually go closer to 2ltrs per day. On my ten days from Lisbon, I actually used less, under or around 1ltr/day. For my Atlantic crossing, I intend on taking 130litres of drinking wanter in 1.5ltr bottles, spread around the boat, with 40ltrs of non-drinking water for washing up, and rinsing after salt showers lashed to the deck.

I truly believe I will end up on the other side with way too much water, but of course, emergencies have to be accounted for.