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Author Topic: !!science!! and desalination: common notions a myth?  (Read 5970 times)

Sphalerite

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!!science!! and desalination: common notions a myth?
« on: November 03, 2011, 09:52:31 pm »

I can't get my desalination plants to not work.

No, that double negative isn't a typo.  I have so far been unable to make a desalination system not work, even when doing everything you aren't supposed to.

My first attempt was in a salty swamp marsh on the shore, with multiple salty murky ponds:


As a test of what you aren't supposed to do, I built a cistern directly on bare ground:


and filled it through the pump.  On testing with a water zone, the water was fresh:


This wasn't supposed to work, according to the common knowledge of how desalination works.

I tried again in a new location, again building a floor-less cistern, this time right next to the ocean:


Again, the water was fresh when pumped:


Even when I dug out the lower level, making sure the water was in direct contact with raw natural stone as shown:


the water was still fresh:


I did see the strange known bug where water near the ocean could not be raised above the level of the ocean.  Once I dug the floor of the cistern below the surface of the ocean, I could not raise the level of the cistern water above the level of the ocean.  Despite this, and despite being in contact with natural stone and sand walls two tiles away from the ocean, the water was still fresh.

I have since tried this in two more embark sites.  I cannot reproduce the claimed behavior of contact with a natural stone or soil wall or floor turning water salty.  I will attempt a few more times, but I'm starting to think that 'cisterns must have constructed walls and floor' is a superstition with no bearing on reality, similar to the claim that dwarves would stop drinking booze if only one type was available.

The closest I've found to validating this claim is on a seaside embark with an aquifer.  The aquifer is salt water, and if I permit the cistern water to come in contact with the aquifer the cistern turns permanently salty.  If I dig a cistern down to the level of the aquifer, the cistern is salty, but if I dig the cistern down one level shy and fill it by a pump, the cistern is fresh water, despite being in direct contact with sand walls:


Comments?
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acetech09

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Re: !!science!! and desalination: common notions a myth?
« Reply #1 on: November 03, 2011, 10:02:29 pm »

I KNOW that water can re-salinate under certain conditions - I kept trying to figure out why my wells weren't being used, until I realized that one of the stairs that the water flows through was carved and not constructed - I drained the cistern, constructed the stairs, and the injured dwarves drank the water fine...

Perhaps certain biomes/conditions don't trigger re-salination, or perhaps that's just a bug you have?
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Sphalerite

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Re: !!science!! and desalination: common notions a myth?
« Reply #2 on: November 03, 2011, 10:06:48 pm »

I KNOW that water can re-salinate under certain conditions - I kept trying to figure out why my wells weren't being used, until I realized that one of the stairs that the water flows through was carved and not constructed - I drained the cistern, constructed the stairs, and the injured dwarves drank the water fine...

Previous experiments suggest that once a tile has contained salt water, any water in that tile will be salty, so it should be impossible to drain, fix, and rebuild a cistern if it was contaminated.  That might be wrong too, so I'll test it.  Also, wells always yield drinkable water even if they're built over salt water.  I suspect your cistern was never salty, but your well may have needed to be deconstructed and rebuilt before it would work again.

Quote
Perhaps certain biomes/conditions don't trigger re-salination, or perhaps that's just a bug you have?
Perhaps, but I have had the exact same results on 4 different embark sites so far.
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Diamond

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Re: !!science!! and desalination: common notions a myth?
« Reply #3 on: November 03, 2011, 10:15:37 pm »

From my previous investigations, basically how pumps work (at least in 40d, but I doubt Toady changed anything):
They destroy salty water and spawn same amount at the pump output title. When water is spawned a check is made too see if output will be salty, and looks up the parameters of output tile. Therefore you can construct walls (and maybe floor too) of said tile of "good" material and after that you can keep your water supply in cistern of pure salt without it becoming salty.
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acetech09

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Re: !!science!! and desalination: common notions a myth?
« Reply #4 on: November 03, 2011, 10:22:06 pm »

I KNOW that water can re-salinate under certain conditions - I kept trying to figure out why my wells weren't being used, until I realized that one of the stairs that the water flows through was carved and not constructed - I drained the cistern, constructed the stairs, and the injured dwarves drank the water fine...

Previous experiments suggest that once a tile has contained salt water, any water in that tile will be salty, so it should be impossible to drain, fix, and rebuild a cistern if it was contaminated.  That might be wrong too, so I'll test it.  Also, wells always yield drinkable water even if they're built over salt water.  I suspect your cistern was never salty, but your well may have needed to be deconstructed and rebuilt before it would work again.

Quote
Perhaps certain biomes/conditions don't trigger re-salination, or perhaps that's just a bug you have?
Perhaps, but I have had the exact same results on 4 different embark sites so far.

I never re-constructed the well... I was under the impression that salt was a contaminant that a well couldn't filter.
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Sphalerite

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Re: !!science!! and desalination: common notions a myth?
« Reply #5 on: November 04, 2011, 07:34:28 am »

I never re-constructed the well... I was under the impression that salt was a contaminant that a well couldn't filter.

From my experiments, it appears that a well will always be usable no matter what kind of water it is placed over.  The water could be salty or murky yet the well will still work and be usable for producing water.  It seems that dwarves will always drink water out of a well.  I'm going to run some more tests to verify that however.
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Quietust

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Re: !!science!! and desalination: common notions a myth?
« Reply #6 on: November 04, 2011, 07:41:28 am »

DFHack's "probe" tool might be of some use here - every map tile has a flag indicating whether or not it is "salty" (and another one for whether or not it is "stagnant").
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Il Palazzo

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Re: !!science!! and desalination: common notions a myth?
« Reply #7 on: November 04, 2011, 08:17:41 am »

Mountainhome Times
7th Slade, 1051; 4,50 U

BREAKING NEWS!

Scientists at the Urist's Institute of Technology discover new facts about dwarven engineering principles that very well might change the way the forts are built.

We talked to the leading sciencist, Sphalerite, PhD:
Sph. - "Dwarven construction regulations are riddled with countless superstitions about what can and what cannot be built. Our team set out to work out the real science behind each of these myths. In our latest paper we pretty much invalidated the traditional approach to water desalination plants.
It is my humble opinion that our work might revolutionise the way our forts are constructed, saving time, materials and most likely also countless dwarven lives."

The paper describing the discovery regarding the desalination plants appeared in !!Nature!! two months ago and is already causing a commotion among old-guard fortress overseers and general labour force.

While the overseers try to discredit the discovery as "an elven conspiracy", the miners and masons begin to show their discontent with having been forced to do what they deem "a pointless, yet dangerous job" constructing saline-proof tanks.

Few of the disgruntled groups set out to occupy the booze stockpiles. Forts of Chamberboats, Cloisterbanner and Whippedgranite have since been all but paralysed by the protesters threatening to remain idle and focus their collective efforts on drinking all of the supplies, unless their ill-defined demands are met.

More as the events unfold.
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Sphalerite

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Re: !!science!! and desalination: common notions a myth?
« Reply #8 on: November 04, 2011, 12:14:59 pm »

DFHack's "probe" tool might be of some use here - every map tile has a flag indicating whether or not it is "salty" (and another one for whether or not it is "stagnant").

Last time I installed DFHack it set off my computer's virus scanners.  Is the current version actually clean and safe to use?
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Wannazzaki

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Re: !!science!! and desalination: common notions a myth?
« Reply #9 on: November 04, 2011, 12:19:41 pm »

DFHack's "probe" tool might be of some use here - every map tile has a flag indicating whether or not it is "salty" (and another one for whether or not it is "stagnant").

Last time I installed DFHack it set off my computer's virus scanners.  Is the current version actually clean and safe to use?

It's always been safe to use. How it edits the running exe causes virus scans to ring sirens. It's all false positive.
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Sphalerite

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Re: !!science!! and desalination: common notions a myth?
« Reply #10 on: November 04, 2011, 12:31:25 pm »

DFHack's "probe" tool might be of some use here - every map tile has a flag indicating whether or not it is "salty" (and another one for whether or not it is "stagnant").

Last time I installed DFHack it set off my computer's virus scanners.  Is the current version actually clean and safe to use?

It's always been safe to use. How it edits the running exe causes virus scans to ring sirens. It's all false positive.

Unfortunately, that still means I can't use it.  I keep my DF files on a thumb drive that I also use to transfer files at work.  The work machines automatically scan installed media for viruses, and any positive matches get reported to the IT department.  I've already been yelled at once for setting off the virus detector just by having the DFHack files downloaded, even though I wasn't actually using them at the time.

I'm also not completely sure that I trust that it really is a false positive.
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blake77

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Re: !!science!! and desalination: common notions a myth?
« Reply #11 on: November 04, 2011, 12:59:43 pm »

I think the current plugin version of DFHack does not trigger the virus scanners.
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cikulisu

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Re: !!science!! and desalination: common notions a myth?
« Reply #12 on: November 04, 2011, 02:05:00 pm »

DFHack's "probe" tool might be of some use here - every map tile has a flag indicating whether or not it is "salty" (and another one for whether or not it is "stagnant").

Last time I installed DFHack it set off my computer's virus scanners.  Is the current version actually clean and safe to use?

It's always been safe to use. How it edits the running exe causes virus scans to ring sirens. It's all false positive.

Unfortunately, that still means I can't use it.  I keep my DF files on a thumb drive that I also use to transfer files at work.  The work machines automatically scan installed media for viruses, and any positive matches get reported to the IT department.  I've already been yelled at once for setting off the virus detector just by having the DFHack files downloaded, even though I wasn't actually using them at the time.

I'm also not completely sure that I trust that it really is a false positive.

my reply consists of equal parts "then stop putting it on the thumbdrive, hit your IT department they are ridiculous, and yes, it's entirely safe and you are being a ninny."
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Sphalerite

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Re: !!science!! and desalination: common notions a myth?
« Reply #13 on: November 06, 2011, 05:38:23 pm »

A quick test of desalination via well:

I embarked on a seaside site, bringing along plenty of wood, some stone, some ropes, food, and no booze.  I verified that activity zones on the oceanside and around the murky pools could not be designated as water sources, indicating that the water was salty, and therefore undrinkable without desalination.

I built half a dozen wells, three along the ocean and three in various murky pools.  All of these wells showed as 'Active', meaning that they were usable as water sources.

Spoiler (click to show/hide)

Note:  I did not set water source zones around the wells.  Activity zones set as water sources are a completely different function than wells.  It is not necessary to set a water source zone around a well, the dwarves will go and use any active and non-forbidden well as a water source.  I did however try setting water source zones around the map to make sure the water was salty.

Very soon after the wells were built, thirsty dwarves began using them to get water:

Spoiler (click to show/hide)

The content of the buckets showed as 'Water laced with salt':

Spoiler (click to show/hide)

Despite the water being salty, the dwarves didn't seem to get any bad thoughts from drinking it.

Spoiler (click to show/hide)

In addition to the well over the murky pool, I also did the same test with buckets set directly over the ocean, with the same results.

I don't know if there are any specific bad thoughts or health effects from drinking salt water for years, other than the general slowdown and increased length and number of breaks from alcohol deprivation.  I also have not tested if salt-water wells are usable as a source of water for prisoners or convalescing injured dwarves yet.  If water from a well is always usable, there's no need to build pump-based desalination systems at all.

It does seem to still be the case that while wells don't desalinate water, dwarves are willing to drink water drawn from a well over a salty water source.  You also can't judge whether a well will be usable by the ability to designate a water source zone around the well.
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Sphalerite

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Re: !!science!! and desalination: common notions a myth?
« Reply #14 on: November 06, 2011, 06:31:21 pm »

I injured one of the dwarves in the seaside embark, and created a minimalist hospital to treat him with.  Another dwarf went to the well and filled a bucket with salt-laced water to wash his wounds.  When he became thirsty, another dwarf fetched a bucket full of water laced with salt to give him.  He now has the 'received water lately' thought and is no longer thirsty, so it appears that water from a well over an un-desalinated salty water source is perfectly usable to wash wounds and give to thirsty dwarves.

I don't know what long-term effects from using salt water to wash wounds or keep injured from dying of thirst, but it appears that at least in the short term desalination with a screw pump is unnecessary.  You only really need it if you're keeping tigermen or other creatures that need to drink, but won't use a well or drink booze.
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