If you have ever watched shows like Alone or Naked and Afraid you know that potable water is rarer than you think and bad water is potentially deadly. Calling a failed roll a "can't find safe water; want to chance it anyway?" is better than "you failed to fill your canteen."
That said I don't think D&D works particularly well as a survival game and if Level Up isn't dramatically changing that aspect it probably isn't worth worrying too much about.
You're definitely right that D&D doesn't work as a survival game... but I don't think that's really the -point- of the Journey System.
Think of the Lord of the Rings Trilogy. You've got the One Ring at the start of the game and you have to get it to Mount Doom. 5e D&D has travel times, some weather effects, vehicles, and random encounters. You could kind of develop a campaign that hits the same beats as the Fellowship of the Ring and such.
But with the Journey System, you've got a much -deeper- ability to do that campaign. Different conceptual regions with Social and Exploration encounters added to the encounter table, a simple method of tracking food and water, like Frodo and Sam in their last days of near-starvation as they struggled, exhausted/fatigued/striferidden, up the slope of Mount Doom itself.
It makes for a deeper, richer, story. And a deeper, richer, world.
And it doesn't -just- work for the Journeyquest style of adventure. Imagine a West Marches game where each Hex you explore gets to be a different tier and land type based on the ones around it. Where the party's Ranger spends the travel time "Scouting" to tell you what the 3 forest hexes to the Northwest, West, and Southwest are in Journey Terms (Deep Feywood, Gentle Feywood, and Deep Feywood) so you can make an appropriate decision about which path to take.
Also I definitely like the "Can't find Safe Water" risk thing. Especially with D&D's various diseases as options. Then again, the spell "Purify Food and Drink" probably still exists, so "Can't find Safe Water" becomes "Found Water!" which means there's no chance to fail...
Might be best to let the DM drop the "Safe" water thing in specific regions/storypoints.