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[Hans Lemurson]

In my last fortress I got annoyed by continuous fuel shortages and the aquifer that was flooding my otherwise plentiful coal-fields so I vowed to start a new one in a VOLCANO!!!  I have no fuel problems now, but am unfortunately rather short on what was once over-plentiful: Water.

I was a fool and did NOT drain my "murky pools" into nice safe underground cisterns first thing upon arrival (I was having too much fun with magma smelters and large aluminum deposits) and so when I finally got around to doing some dwarven farming, I found that I had not a single drop of standing water on the entire map.  Actually that's not quite true: a small lake on the higher altitude regions of the volcano (cooler climate?) was still wet which explained where all the turtles kept coming from without having to resort to recursive cosmological theories.

So here I was, thanking the gods that I've had no injured dwarves yet when I got an announcement that it was now the Rainy Season and soon enough it had begun to rain.  "Hey, I think I remember reading that murky pools will refill with rain."  And as I looked, the largest pool in on the valley floor started turning beautiful blue again.  I quickly dug some drainage off to the side to capture as much as possible before it began to evaporate again and ended up with about 30 units of water in a 7-tile cistern.  Not...too bad, but hardly sufficient.  I then cried a few mournful tears as the bountiful clouds ceased their priceless gift and the puddles started to vanish from my water source.

The next year, I was better prepared to catch water, but the rains seemed to be not quite as forthcoming as in prior years.  I had in the mean time managed to set up a prickle-berry farm at the mouth of my fortress and so was in no danger of starvation, and the incredible mineral wealth of the volcano would let me buy out entire caravans with a few well-made Aluminum goblets, but I was still haunted by the paltry amount of water I had in storage.  Not even enough to USE, because if it falls below a critical threshold of depth, then normal evaporation will begin to take its cruel course and bring mocking doom to my pathetic attempts to collect this priceless treasure from the skies.  It's ironic that with all this wealth, I can't buy the simplest of substances.

So the third came and I felt that I had enough water in storage that I might be able to let my dwarves at it.  And then the second cruel irony struck: It was all brackish water.  Or so I assume from reading the wiki given that placing a zone around my cistern yielded a count of ZERO tiles suitable for a water source.  The embarkation screen HAD warned me that this place had salty water, but I assumed that that was due to the little piece of beach-biome that I snagged which turned out to be just a small area filled with andesite-pebbles and driftwood(is it harvestable?) without any ocean.  The murky pools are very much in the main biome, and all have brackish water.

So...what do I do?  Here are my questions:

1) How does desalination work?  I've read about it and even constructed myself an artificially-lined cistern out of the finest alunite blocks to differentiate it from the microcline it was dug into, but I simply don't have enough water to test it out. Which brings me to my next question.

2) What is the most efficient way of collecting rainwater(especially in a hot climate)?  I only manage to extract about 1/4 of the rainfall that lands in my pool each year and I can't really think of a way around this.  If I put gratings over the pool will rain still come through? Will this reduce the "hot climate outdoors evaporation" effect?

[FleshForge]

Just drill a well.  Unless you're amazingly unlucky, there will be water down there somewhere, probably more than one source.  Fishing too, if you're bold!  Beware flying/swimming underground critters though.

[Hans Lemurson]

The embark report also claimed that there was an aquifer but after extensive digging I think it merely mocks me.  As for finding water, there's good news and bad news.

I have dug down and found a large cavern.  A MASSIVE cavern.  My starting location is at z-level 105, the roof of the cavern is at 89, and the floor is at...-3.  In fact, I just learned that Z-levels can go negative.

At the bottom of the cavern is a lake.  Happy times.  It is however a finite water resource.

I've just constructed a well-hole over the pool through 40 z's of solid rock which breaks into the cavern at 60z and plunges through the abyss into the negative zone.  Will my dwarves be able to get fresh water from this?

Also I am contemplating building a 100z tall pump-stack carved through a thick cavern column.  After a brief amount of "fun" involving floodgate controls made from less-than magma-safe building materials, I determined that I could not in fact build a magma-based perpetual motion machine to power the pumps from the top (the water wheel wouldn't turn... ).  I was then faced with a chicken-egg situation of "I can't make water-reactors without water and I can't pump the water up 100z's without a power plant" until I had a head-smacking moment and realized that I can build the reactors at the bottom (where the water already is).

So...I probably have access to water now, but it's still a finite source, only about 2,000 units of extractable water, and closer to 1,200 if you take into account losses in the pumping process and if I don't want to drain the lake to critical levels and destroy it.  It's a sizeable amount, but doesn't leave anything left for some of the more...dwarven uses of large volumes of water.

Has anybody had any experience with efficient rainwater collection?  How about desalination?  At my current collection rate it'll be bout 5 years before I can begin experimenting with desalination.

[FleshForge]

At the bottom of the cavern is a lake.  Happy times.  It is however a finite water resource.

If it touches any map edge, I actually don't think that's so, I think it's infinite.  If it's an enclosed lake, then no.

Wells can be any depth, although it does take time for the bucket to travel up and down.  You can, however, drill as many wells as you like, at the cost of the parts for each (not a big deal really after you get a bit settled).

There's nothing says you can't use windmills, although that's probably going to need a whole lot of windmills to pump water that far.

I understand that if you place a well over salt water, dwarves will drink it and not be bothered - while this is almost certainly a silly bug, it's also darn convenient.

[Hans Lemurson]

It is a fully enclosed lake.  It's actually in two parts which I just joined together and there has been a drop in the water level.  Lots of little 6's skimmering around a big pool of 7s.

Do wells really make brackish water ok to drink?  I read somewhere that they used to but don't any more in 31.12, but I guess the best thing to do is Dwarven Science.

Any rainwater collecting wisdom though?

[Laurin]

Water from Murky pool is good, if the pool is deeper than 3, I think.

Pumped Saltwater is automatically desinalinated. But you must build a reservoir with constructed floors and constructed walls, otherwise if the water touches any unconstructed material it will instantly be salty again.

[Psychobones]

Desalinization is simply just running the water through a screw pump into a prebuilt cistern. I personally wasn't 100% sure what it could and couldn't touch, so I lined the whole area(flooring and all). Link the pump to a windmill or a waterwheel, and your golden. But be sure your cistern is large enough for all your water. My only saltwater fort died because I tried pumping too much water into the cistern, it overflowed and all became saltwater as soon as the overflow touched land.

Your aquifer might only exist on a certain patch. I personally have an aquifer under only about half my fort, my metal industry sits just barely outside the aquifer, otherwise I'd have obsidian instead of magma powering my forges. As they're usually the border between sand and metal, it might be above you as opposed to below if you built into the mountain of the volcano. Or it might only exist on a small chunk of your map. Note, unlike real life, if your water is saltwater, then your aquifer is saltwater. Not sure if that's true for cavern water though.

Collecting rainwater has never been an issue for me, as I don't think I've tried a scorching or hot biome. However, if it works anything like real rain, a giant funnel might be your next creation.

[FleshForge]

As far as I've seen, only surface pools ever collect rainwater, and that is dependent on terrain and climate - if they are staying dry over the course of a year, then probably they're just gone, period.  Explore around some more in the caverns (there are 3 layers by default) and look for more water, unless you're really terribly unlucky there will be more and probably unlimited.

[Khift]

A 94 z-level cavern? This I gotta see. What did you do to the worldgen parameters to get such a monstrosity?

[Hans Lemurson]

A 94 z-level cavern? This I gotta see. What did you do to the worldgen parameters to get such a monstrosity?

I didn't do anything, I swear! I'm innocent I tell you!

My rainwater source is a 55 tile irregularly shaped murky pool.  Murky-pool bottoms are a unique terrain type which as far as I know cannot be replicated.  When a drop of rain hits them it becomes 1 unit of water as opposed to dissipating like it does on every other type of terrain.

I have dug out a cistern next to the pool one z-level below and have carved channels that feed into the cistern along its perimeter safely underneath the overhang so that they are listed as "underground".  I am also in the process of carving a channel from my meager cistern over to where my constructed freshwater pool is so that I can then pump water into it, but don't yet have enough water collected to proceed with this.  I have about 100 units of water in storage but I won't feel comfortable pumping any until I've accumulated 400 units (which will fill the completed channel up to level 7).

For my pumping project, I'm setting up a pump-parts stockpile at the base of the "pillar of suitable thickness" and am coming to grips with the prospect of a 100 level pump-stack.  It will require the combined power of 7 full water reactors to power this monstrosity, and to avoid water losses due to the puddles (a volume equal to the total amount of rainwater i have collected so far) that will remain in the stack it'll have to be all in one go.

Metal is plentiful, but still my total materials costs are looking something like:
110 screw pumps (103 for the stack, 7 for the water reactors):
-110 Blocks (I've been processing Basalt like crazy, so check)
-110 Giant Corkscrews
-110 Pipe Sections
--That means 220 units of metal...which I have because I'm living in a Volcano.  I have native copper coming out of my ears as well as plentiful hematite.
14 water-wheels
-42 pieces of wood
--I've got plenty of wood.  In fact I've been just buying most of mine from caravans rather than chopping it myself because my consumption rates have been so low.
I'll also need some mechanisms for gears to turn my pump-stack on and off and a bit more wood for whatever axles I might need.

...Does this count as a mega-project yet?  Probably not because it's only really moderate in size and actually serves a useful purpose.

[sockless]

If you really want to, you could cheat a bit and use DFhack.

[Hans Lemurson]

If I wanted to do things the "easy way", then I wouldn't be playing Dwarf Fortress.  My embark also has no sand or flux-stone so lack of water isn't the only challenge I'm facing.  However unlike water, those things can be purchased.

Actually, those three lacks are the only challenges I'm facing since igneous extrusive layers are so darned abundant in valuables.

[Hans Lemurson]

Update:

Digging deeper, I have found 2 more caverns (each 2-3 zlevels in height) , each with their own pools of water, but I have yet to determine whether they are finite or not.

I also had my first goblin siege, and so now my first injuries.  Fortunately my long well that dips at water 100 units below it seems to be providing some water...but the description of the bucket contents held by my medical dwarf say that it's "water laced with mud".  Is this normal for well-water?

[fivex]

Can you upload the save-file? I'm asking mainly because of the 94 z-level cavern.

[Hans Lemurson]

Sure. 
...How do you do that?