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[gchristopher]

Since updating to 34_05, I've been unable to fill a large cistern with water using a pump stack to bring water up to the top, then flowing into the cistern. The water seems to compress into itself, filling only the lowest z-level of the cistern.

The cistern is just a 4x4 hole with a pump stack bringing water up from a lake and dumping it down into the cistern. The drain is from the underside of an adjacent lake to the bottom of the pump stack, so there's plenty of water being pumped, close to the capacity of the pump. After the lowest z-level fills almost instantly, the water keeps falling, but the second z-level never starts filling. It's powered by a water reactor, so much of the nearby lake has been lowered from all the water disappearing into the cistern.

Has anyone else had a problem like this?

UPDATE: This is a known issue on a map with a lake or ocean dating back to 40d at least. Cisterns above or below sea level work fine, but cisterns that cross sea level vertically cannot be filled above sea level. (Possibly the distance from the ocean matters?)

40d: Can't pump water above sea level
Vanishing Water (Help!)

[Radiant_Phoenix]

Do you have an aquifer?

[gchristopher]

There is an aquifer in addition to the lake, but it's nowhere near the cistern. I was building it to supply pressurized water for traps and plumbing.

[gchristopher]

I tried depressurizing the inlet by putting a diagonal between the pump and the cistern in case it was some glitch with pump-induced pressure. No luck, the first z-level of water in the cistern "eats" any further water that falls in, and the second z-level never starts to fill.

[NecroRebel]

The water has to be going somewhere. If any of the wall tiles of that cistern are tagged as aquifer, they can eat a limitless amount of water, even if they're completely isolated from the rest of the aquifer. Alternatively, the water might be pressure-teleporting elsewhere if there's any way for it to do so. Without being able to actually see your setup, though, it's basically impossible for us to troubleshoot. Screenshots, perhaps?

[slothen]

i hear beaches near oceans behave similar to aquifers in their water-eating capabilities.

[gchristopher]

Thanks for taking a look! I appreciate it.

The first z-level does eat water just like an aquifer, filling to 7/7 and absorbing all water beyond that. However, the interior tiles were all dry stone when dug, so there definitely wasn't any aquifer-like source of water in the process. (Though a wall adjoins the lake.)

Here are screenshots. Ironhand graphics pack.

This is Z-0, the base of the cistern. (Some features torn out for making this test simpler.) The walls are all smoothed or constructed stone, plus a door and a floodgate. The floors are all constructed floors. To the west is part of the pump stack. The bottom of the lake to the south ramps down to feed the pump stack.

I'm certain the walls and floor are solid and no water is leaking to any place on this or lower z-levels.

Z:0 before pumping


Here is Z-level +1. It's just smoothed walls around open space.

Z:+1 before pumping


At Z-level +10 is the top of the pump stack where water flows into the cistern. Pretty straightforward.

Z:+10 before pumping


That's the setup before the pump stack is activated, letting water flow into the cistern. Once the pump is running,  Z-level 0 rapidly fills to 7/7 in all tiles:

Z:0 after a little pumping


On Z-level +1, there's lots of falling water. (The pumps are fast enough that there's sometimes 4 columns of falling water coming down.) However, none of the tiles except the ones directly under the falling water ever seem to even reach 1/7 water. Instead, it all instantly vanishes into Z-level 0.

Z:1 after lots of pumping


It really is like some kind of invisible water-destruction-only aquifer that exists despite all smoothed or constructed stone being used in every tile involved.

I tried probing all of the tiles with dfhack (which was quite boring) and none of them had bits.water_table set, or differed in any way other than being in several different biome numbers, but I have little idea what those mean. This point is vaguely at the meeting point of mountain, lake and swamp biomes, but there's 6 different biome numbers reported. Maybe the river is in play somehow too?

Any suggestions about anything else I can do to diagnose it?

[gchristopher]

I tried building a floor on Z +1, and that allowed the cistern to fill! There's definitely some kind of invisible aquifer-like behavior specific to that Z-0 level. Thanks for the clue.

With dfhack probe's help, I'll split it into smaller cisterns that all fall within the same biome number reported by dfhack (whatever that means) and see if the ghostly aquifer effect is specific to any of them.

[gchristopher]

No luck. All the biomes appear to share the aquifer-like water-eating property at that z-level. I guess it's just impossible to pressurize water on that level. It's at the same level as the lake, so maybe there's something to do with how the game maintains the lake height? Maybe I could try again (ouch) some distance from the lake?

I'm starting to think this rises to the level of a bug report. Am I way off on something?

[robertheinrich]

Upload your save to somewhere, so we can take a look at it. Filling a cistern to a level higher than the river/lake the water comes from should not be a problem.

Just a comment: you donīt need such a huge cistern, by the way. 3x3 or maybe 5x5 and a few z deep will provide your fort with enough fresh water for years and years. Currently I have a 4x4 cistern and over the last 2-3 years (with ca. 100 dwarves) the top waterlevel only sank from 7 to 6. So they used about 16 units of water. On the other hand almost nobody got sick or injured so far.

[Sphalerite]

I have seen this behavior on sites with an ocean.   When you pour water into a cistern that includes a Z-layer at the same layer as the surface of the ocean, any water poured above that surface simply vanishes.  I suspect lakes may do the same thing.  If it's the same bug, you won't be able to fill water over the level of the lake anywhere on your site.

[MarcAFK]

That sounds reasonable, except his new cistern starting on the floor above the lake is filling fine.

[Sphalerite]

Right.  You only see the problem when you have a layer of water at the same layer as the local water surface.  A cistern which is completely above sea level will work fine.  A cistern which is completely below sea level will work fine.  A cistern which is partly above and partly below sea level will not fill above sea level - any water you put in over sea level will simply vanish.  This bug has been around for a while.

[MarcAFK]

Oops, i misread your post, i just skimmed the last line and got confused.

[gchristopher]

...  A cistern which is completely below sea level will work fine.  A cistern which is partly above and partly below sea level will not fill above sea level - any water you put in over sea level will simply vanish.  This bug has been around for a while.

Thanks! Adding "sea level" to my search for vanishing water turned up the threads I couldn't find when I searched initially. This bug/behavior dates back to 40d, at least. I was searching for only recent results; since this bug wasn't mentioned on the wiki, I presumed incorrectly it was new to DF2012.

A couple prior threads:
40d: Can't pump water above sea level
Vanishing Water (Help!)

Those threads and the example save suggest that a cistern located farther away from the shoreline will avoid the effect. Do you know if that claim was tested? I guess my long-suffering dorfs can be recruited to go build another cistern to try it.

Upload your save to somewhere, so we can take a look at it. Filling a cistern to a level higher than the river/lake the water comes from should not be a problem.

Looks like someone made a demonstration save for that purpose in 2009.

Just a comment: you donīt need such a huge cistern, by the way. 3x3 or maybe 5x5 and a few z deep will provide your fort with enough fresh water for years and years. Currently I have a 4x4 cistern and over the last 2-3 years (with ca. 100 dwarves) the top waterlevel only sank from 7 to 6. So they used about 16 units of water. On the other hand almost nobody got sick or injured so far.

Yes, that's far too much water for drinking and hospital/prison use. However, it's only slightly overkill for feeding the high-pressure goblin wash / trap hallway cleaner system that feeds into an automated water atom smasher. Also, the obsidian casting facility consumes 2,800 water per use.

Sadly, all of the plumbing and machinery for the high-pressure water systems are already built, but can't be pressurized now. I think that's probably the end of the line for this fortress.