I was thinking about survival on small islands in the ocean. One of the first things they tell you about survival: find water. Follow a stream to a spring, etc.
So you find yourself on an island in the middle of the ocean. It’s small but not too small for survival. There are trees growing, etc.
Could you expect to find a spring on such an island? Or would you have to depend on rainfall for water? What would be a good strategy for storing water either from the spring or from rain, assuming you arrived on the island with only the clothes on your back?
Quite a few “Deserted Islands” have no source of fresh water, other than rainfall. They are too low for a spring. This is generally why they are deserted.
One “good” thing is that your little island likely has lots of plastic crap washed up, including bottles. Rinse them in salt water, then use a tarp* to catch rain. Go crazy, fill every bottle, since it might not rain for six months.
Note that the much vaunted "solar still’ made by digging a pit and putting a part over it is useless. You lose more water making one than you can gain. Mind you some lifeboats come with a ready made one that uses the ocean, and they sorta work.
you are going to find more plastic to use for a 'tarp".
Many islands lack fresh water. Heck, they named the Dry Tortugas ‘dry’ because they had no fresh water. Yet people settled on them anyway (well, a military base was built), and built elaborate rain collection and storage devices.
Any potable water you find on the Dry Tortugas was probably shipped there. With Florida being so close, I can’t imagine that even the Civil-War-era army would depend on rainfall to ensure survival.
I saw plenty of cisterns when I visited Ft. Jefferson, and the park rangers telling of the history told how the residents depended on rainwater collection to raise crops in their garden plots.
If you have a waterproof trash bag, tarp, leftover rubber life raft, etc, these can be useful for catching and storing rain. Dig a hole and line it with the waterproof item. Captured and stored this way, you risk lots of stuff being blown or washed into the water and you might want to boil it before you drink it, but at least you have it.
And I wouldn’t write off the solar still idea quite so quickly as Dr Deth does. It’s not a very efficient way of getting water, I agree, but the amount of water (sweat) you lose digging it will depend a lot on the conditions of your specific situation. Built at night, in sand, with proper tools, I can see it being a net positive. The longer you’re stuck on the island, the more net benefit you get from it.
One last thought I have: sometimes fresh water can be underground. On a deserted island, I’d look for areas where plants might be accessing fresh water through their roots and then see if I can’t get to that water without excessive effort digging. One problem with this idea is that I’m told water can be too salty to properly hydrate you, but not salty enough for you to taste it.
there’s reasonable ways to desalinate sea water, enough for drinking. But yes, you’d better take the needed gear for catching and storing rainwater. Also, anyone who has to ask such questions better STUDY such a life, for at least a year, then experiment with it part time, before taking the plunge. better have a satellite phone and a boat-owner checking on you there, too, regularly!
On Bermuda, residences have rainwater collection systems. Roof runoff flows into gutters and eventually into holding tanks for later inside use.
I recently visited an island in New Zealand where the same practice was used. On this island, a not too long ferry ride from a major city, a local told me that it was common to need to top-up one’s tank during the dry season from a water truck. On Bermuda, not sure if that’s available.
It’s really not any different from springs anywhere. Rain takes time to move through soil. (Heck, even rivers and streams often move at just a few miles per hour). So during a good rain, you get some immediately runoff from water on the surface, and some long-term runoff from water that moves along underground for a while before (in the case of a spring) finding a way to the surface. Sometimes that happens when you have a non-permeable bedrock layer with something like sand on the top. At the point where the sand has eroded away to expose the bedrock, the groundwater turns into a spring.
The bigger the island, the more likely it is to have some kind of a spring. The Far Side style island with its two palm trees is not going to have a spring.
The only way you could “lose” water from digging a solar still is through sweating.
On a morning with an ambient temperature of 0oC, digging a hole a foot deep and 3 feet across in sand will cause you to lose approximately no sweat at all.
You are on an island, so you have an infinite source of seawater to keep the sand in your hole saturated.
Based on experience, the yield from a solar still in saturated sand exposed to full sunlight on a day with a maximum temperature in the mid twenties will be about a litre. They can apparently yield 1.5 litresor more, though mine have never been that successful
There is just no way you could lose 500mL of sweat digging a hole in sand on a cold morning, much less two litres.
While I am sure there are plenty of circumstances where you *could *lose more water constructing a still than it produces (Being stupid enough to dig in the middle of a hot day. Hard, dry, clay soil) your blanket declaration that you must lose more water than a still could produce is flat out wrong.
Of course! What would be the point of the winding key otherwise?
Seriously, though, an island won’t have a spring if it lacks the essential ingredients – enough height above sea level (and the necessary ground structure) to allow a fresh water table, enough land area to collect rain water, and enough of a height difference to allow the water to concentrate.
Aruba has what it needs --p barely. It has not a huge amount of rainfall, it’s got enough land far enough above sea level, and it has height differentials, most notably Haystack “mountain”, to allow the water to flow into a few collection points. But there’s not enough fresh water on the island to support a large population or agriculture. Aruba really became habitable when the oil companies exploiting the offshore oil decided to put in desalination plants for the workers living on the island and working the refinery. That allowed the tourist industry to get a foothold and eventually take over. But without desalination plants Aruba would be nothing.
What’s the largest island to lack adequate fresh water to support a sustainable level of human habitation? I note some pretty good sized ones off the west coast of Mexico (Maria Magdalena and Maria Cleofas) that seem pretty uninhabited and I suspect lack of fresh water’s probably the reason.
You can lose up to 2–4 liters per hour on a hot day, like of a desert island. Most experts have found a still produces maybe a cup.* A day.* 240Ml. In other words, you lose 10 times as much as you get back.
The problem with using wet ocean sand is that you get salt in your water.
The system is inefficient for how much work is put into it versus the water output.[5] In desert environments water needs can exceed 1 US gallon (3.8 L) per day for a person at rest, while still production may average 8 US fluid ounces (240 mL) per day.[5][6] Even with tools, digging a hole requires energy and makes a person lose water through perspiration; this means that even several days of water collection may not be equal to the water lost in its construction
Sure they can if you have a "Three insulated hot-box solar earth-water stills were
constructed (see Fig. 2). Each had a collection surface of
two-thirds square meter glass (67 em x 100 em). "
Your study didnt test the simple hole in the ground survival still. No doubt, altho the labor is much greater, a well constructed solar still as they used will eventually provide more water than is used by making it.
I was talking about "the much vaunted "solar still’ made by digging a pit and putting a tarp over it ". Not some structure made of wood, glass, etc and used for long term water retrieval.
Sigh. Doctor Death is back to his old tricks. Make a ridiculous pronouncement, then spend days weaseling around to get out of it.
Try reading again. Those were figures for a simple hole in the ground.
You didn’t say you might possibly lose more water in 24 hour day than you can get from a solar still. You said that you will inevitably lose more water from building a still than you ever can get back from the still. That claim is utter bollocks.