What if we could drink ocean water?
Let us ignore the existence and effects of other species.
And let us assume that no new water would be created.
Given current consumption, how long would our species last before water ran out?
Presumably we would pee out water, like we do now?
I don’t get the question, you seem to be missing some more “what ifs” and “buts” that you may want to add later.
We can drink fresh water. We can drink water with some things dissolved in it. We can drink water with a great deal of salt in it, but we need fresh water soon. Ocean water isn’t toxic to humans, I drink it when I go to the beach, and have fresh water later. In a survival situation, with nothing but ocean water to drink, we’ll die, and rapidly.
What situation, that I described above, do you want to change? What’s the “water created part” in your premise mean? We can only drink ocean water, never collect rain water and drink fresh? That humanity will drink the ocean dry because there’s no water cycle on the Earth?
OK.
Humans can’t produce urine concentrated to get rid of the salt in ocean water if we drank only that. In fact, many animals can’t either. The kangaroo rat, as my high school bio book claimed can do so. It has a number of water saving biology and behavioral abilities. Its a small, burrowing mammal that doesn’t keep its body temperature tightly regulated. Its not a large, bipedal, biocular, carnivorous/omnivorous, fast moving under all circumstances, derived from jungle apes, open savanna dwelling, widely traveling, mammal. I can only conjecture if we had more of the biology and behavior traits to deal with excess salt in water, we wouldn’t have evolved to be sapient beings.
I think it amounts to:
At the rate at which humans (all of them, combined) consume drinking water, how long would it take to consume an amount equal to the volume of all the oceans?
My back-of the-envelope calculation (based on 7.6 billion people each drinking an average of 1 liter a day from oceans containing 1.33 billion cubic kilometers of water) is ~500 million years.
And during those 500M years, how much would the population expand?
Didn’t Thor try something like that once?
If 10 billion people each chug a couple of liters of water per day, an ocean’s worth (say 1.3 x 10^21 liters), it would take a few hundred million years. But was that the question?
Aliens equip every one of us ~8 billion folks with access to two technologies:
- Faucets of clean water designed only for internal consumption (drinking, use boiling food, etc.)
- Toilets designed only for eliminating poop and pee.
The faucets come from a reservoir equivalent to the earth’s oceans. The toilets go to a separate reservoir in an inaccessible extradimensional space.
Humans may no longer internally consume any of the universe’s other water.
Finally, aliens stabilize earth’s population once we reach 8 billion, because they want the calculations to be simple.
How long will humanity survive, if this water constraint is the only limiting factor?
Edit: sounds like others have already phrased it, and solved it, more simply!
Oh.
Some variant of this fast, I’d assume.
From the trivia desk: The world’s oceans contain 15,000 times as much water as the all the world’s freshwater lakes. Still, that’s barely a billion billion liters which leads to the following surprise:
On the morning of the 15th of April, 44 BC, Julius Caesar brushed his teeth. What is the chance that, at some point in your life, you’ve ingested a molecule of water that Caesar used in brushing his teeth on that fateful day?
Answer (if my arithmetic is correct): Every single cup of water you drink has many thousands of such molecules!
Hey! Don’t even think of it; I like to swim in that ocean.
Here’s a related question, which is going to require speculation. If humans could drink ocean water what would that have meant for human migration hundreds or thousands of years ago? When European explorers like Magellan went around the world (and earlier than that, when the Polynesians settled around the Pacific Ocean) they had to carry drinking water with them. Would people have migrated earlier if the trip wasn’t complicated by that requirement?
The way I first heard a certain puzzle formulated is: you have an unlimited supply of fuel at one edge of a desert, but no sources in the middle of the desert itself. Your truck can carry enough fuel to go 500 miles, and you can build an unlimited amount of fuel depots along the way. How many trips will it take to cross the desert? (As a function of the width of the desert)
So you can get arbitrarily far in stages. In real life, though, it is already possible to travel thousands of kilometers in a canoe, and you need good sources of food and water at the destination, otherwise you would not bother settling there in the first place. So I am not sure that different water requirements would have radically affected the island-hopping timeline.
I think it’s a certainty. A 2000 year-old Greek map shows the Ganges River and a ‘land of silk’ to its north. There is some evidence that Roman emissaries reached Indo-China at least 1850 years ago. And Greeks and Romans did know the world was round.
Ships were afraid to venture Westward from Europe not because of a fear of falling off the Earth’s edge but due to a realistic fear of starving or dying of thirst. (Columbus dared … because he miscalculated the westward distance to Asia! :smack: )
[INDENT]*Day after day, day after day,
We stuck, nor breath nor motion;
As idle as a painted ship
Upon a painted ocean.
Water, water, every where,
And all the boards did shrink;
Water, water, every where,
Nor any drop to drink.
The very deep did rot: O Christ!
That ever this should be!
Yea, slimy things did crawl with legs
Upon the slimy sea. *[/INDENT]
This might be fighting the hypothetical but water never runs out on Earth. It may become ice, vapor, sink deep into the ground but it never truly “leaves.” It’s always recycled.
Trick question, he died on the 15th of March, 44 BC, a month before his fateful toothbrushing. Always remember to beware the Ides of March.
I’m equally interested to know if the OP believes that the answer to this question (if it’s similar to the xkcd strip) has real world relevance to something. Is it just to get an intuitive feel for the size of the oceans?
:smack: We Americans are so used to worrying about the* Ides of** April***, I got the date wrong. 
The technologies that were needed for serious ocean voyaging include:
- How to build (& sail) ships that could handle all the weather of a long voyage
- How to know your position when out of sight of familiar places
- Enough knowledge of weather and currents to keep voyages to an acceptable duration
- How to keep sailors alive and healthy
Carrying sufficient fresh water is an important, but also rather simple part of all this.
Terry Pratchett, Reaper man:
People have believed for hundreds of years that newts in a well mean that the water’s fresh and drinkable, and in all that time never asked themselves whether the newts got out to go to the lavatory.
This is a great opportunity for me to take someone else’s smartassing even further. The Ides of April are April 13, not April 15. In the Roman calendar, the Ides were the 15th day of the month in March, May, July, and October; in all other months, they were the 13th day.