I must be dead then.
To whom shall I offer my condolences?
Good question. Nobody cares 'bout me or science.
Studies also indicate that horses respond favorably to the air being full of sound.
Daily water requirement of a horse: 20-55 l
donkey: 18-35 l
camel: About 20-50 l, but this is what you want. They lose less water to evaporation, are resistant to heat and dehydration, and can obtain 18-20 l/day solely from their diet. A week in the desert without water should be nothing to a camel.
When he was US Secretary of War, Jefferson Davis tried using camels in the US Army. Supposedly escaped camels lived for many years.
I’m hoping the donkey was named Timothy.
I assume, too, that food is an issue - a horse or cow is designed by nature to spend all their spare time grazing; even if the horse feed was higher-energy stuff than grass, I suspect a small bag of oats is not enough for a 3 to 6 day jaunt.
Yes, they also need barrels of feed in the wagon.
That would have been an interesting episode; planning and co-operating to survive and be able to recover everyone’s belongings.
Horses require more grain, are less tolerant of desert vegetation as food and have far less stamina than a mules or an oxen. Oxen are able to take advantage of poor native feed, have more stamina and were less expensive. While movies always tend to use horses, Oxen are almost universally the recommended option in the guidebooks of the era and were the most common option.
Mules are also superior for pulling wagons compared to horses, and made of a large percentage of wagons which were not pulled by oxen.
https://www.oregontrailcenter.org/HistoricalTrails/MulesOrOxen.htm
Horses were the minority in a historical sense but are far more romantic for movies, books and TV. Handcarts were also more common than a person would typically expect in today’s world.
And the modern take on water is that there’s no point in rationing it, you need as much water as you need. Yet I’ve heard for years that people could “condition” themselves to need less water. Supposedly, Montgomery’s forces in North Africa in WW2 survived and fought on one pint (that’s a Brit pint of 20 Imperial fluid ounces) per day. What’s the Straight Dope on this?
Did they also have a rum ration?
They had an advantage over the Italians in that regard 
I remember in Centennial, in the section about wagon trains west, the protagonists joined a party where the wagonmaster insisted they use oxen for drawing the wagons. Some protested, “But horses are so much faster, they’ll arrive first; all the good land will be gone!”
“No they won’t,” was the laconic reply. The first week or two the horse-wagons were leaving them in the dust and everyone was fussy, then as the weeks passed, they started passing by people stranded with dead horses. They couldn’t be helped because protagonists’ own wagons were already loaded to capacity.
They probably weren’t counting the four gals/day/each tea ration.
I also have it on good authority that you only need to provide for the first eight days, sometime on the ninth day the water issue corrects itself and also by then the horse no longer needs to be controlled. Little known fact, there.
Wild horses manage quite nicely in the desert. Just ask gatopescado.
Those populations cluster around water sources, and more importantly typically around non-native (to the desert) vegetation.
Introduced forage species dramatically increases the AUM/Acre for a bit of land, and wild horses don’t tend to drive to a map location to save a waggon. They will stay around forage and water sources except for times of migration, and they will stop to graze when they get a chance.
Remember that there were zero tumbling tumbleweeds in the US until ~1877. (not that they are forage, but a very visible movie/tv item)
As an example, in Utah
As to “modern take,” and your mention of Montgomery, I presume you are talking about controlled or empirical studies by militaries. Don’t know the SD, but I remember some major turning point many many years ago when the IDF announced some sort of internal study/decision on allowing trained soldiers to restrict, ad-lib, their own water intake, rather than having it rationed by TPTB.
CX: Actually, I have no idea how long–or how true :)–that IDF water policy is.
ETA: Another fine contribution in the category of Leo’s really really useful posts.
While native peoples and animals might know where to find water in the desert, old timey wagon trains (the situation in the OP) are a different matter.
They typically don’t know where all the water sources in the area are. The Meek Cutoff is a notorious example of how things go wrong when you don’t know which way to go to the next watering hole.
Also, even if you know where all the watering holes are, getting wagons to those places can be hard. In addition, it will tack on a lot of extra miles. The additional wear and tear and, more importantly, the extra time to roam around to water sources can be deadly.
The Donner party made one mistake in taking an alternate route and ended up late entering the mountains and bad stuff ensued.
Moving quickly from water source A to water source B was key. That there were other water sources somewhere off the trail is immaterial.