20 litres for a sedate software developer in an air conditioned office, yes. If that dev goes to the gym after work they'd need more! Let alone crossing a desert in the heat.

I'm probably doing 3 litres a day of pure water (plus water from coffees / food etc.) in 30 degree temps, but spending most of that time inside with air-con. It's probably not enough as I am pissing orange still.

Edit: someone like me wouldn't hike in deserts though, so by survivorship bias people that do it often probably need less water to stay cool. But 2l/day even if walking only dusk/dawn seems tight still.

Probably a bit more, considering he was prepared for desert conditions (and probably) some physical work as well