Carrying 10 days worth or water sounds pretty rough, there must be a sweet spot where carrying a little less water actually gets you further.
The standard guidance is 1 gallon (~4 liters) of water per day, via all sources (includes food). A gallon weighs a little more than 8 pounds, so that’s 80+ pounds of water for ten days (not counting container, backpack, and whatever else you’re schlepping). Weight will decrease each day, but that’s a lot of weight up front. Backpackers usually try to carry half that, but 80 isn’t out of the question if you’re conditioned for it (eg US ground military carry 60-100 lbs).
A gallon a day is probably overkill for a short term survival situation, though. Having less, especially while you’re exerting yourself, may cause damage, but the survival goal is just to come out the other side.
Some quick googling on actual minimums to survive turned up this thread, where someone calculated it to be 1 liter per day while resting in a cool environment. So that’s 20lbs that needs to be adjusted upward for carrying significant weight offtrail in potentially hot conditions. https://www.backcountrysurvival.co.uk/2016/05/20/minimum-amo...
If you split the difference and assume strict rationing, you’re looking at 50lb start weight and suffering significant but not incapacitating dehydration. Brutal, but conceivable.
Unless you are in the Italian army, they need more.
Difference is that you can make trips to set up fuel dumps wherever you want.
From the article though it didn’t sound he drove very far, so carry less than 10 days would have been possible too.