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[reilwin]

Again, these would nearly all be solved by a simple check for the "flow" tag.

*shrug

Would it really? What would happen to water reservoirs then which don't employ a flowing water source? Only flowing water can avoid being stagnant? What if a stagnant pool suddenly starts flowing because you're draining it? Is it still stagnant? What if the water from the stagnant pool was drained into another reservoir and stopped flowing?

Your idea is appealing in its simplicity but there are several edge cases which make it a bit more complicated than it seems.

[wierd]

See my original post.

Stagnant water, by definition, is water that isn't flowing. That it usually connotates "yucky" is due to the fact that stagnant water doesn't "breathe" the same way, and accumulates toxins from microbes living in it.

Turbulent water is a harsher environment for micrbial colonies, and is cleaner than stagnant water.  Any water left to stand will eventually become stagnant. This includes wells open to the surface.

In this case, the stagnant water plauge is just more realistic. Moving water is never stagnant though. It can be contaminated, but is never stagnant.

See the wiki page on water stagnation


For stagnant reservoirs, etc, a system to "flush" them, and thus set the "flow" tag should, by the same simple check, remove the stagnant tag from the water.  Eg, to fix a broken well, just flush it occasionally.

[Monk321654]

Isn't there a Bug/Feature where any water obtained from a well is automaticly filtered, or was that fixed already?

[wierd]

That's passing through a screwpump.  Wells can bucket up stagnant water, which greatly increases rate of infection if used by a hospital.

[NW_Kohaku]

You have to completely replace all walls and floors with constructed walls and floors before water touches them, or else they will be marked as "stagnant" tiles permanently if you are using a screw pump, so if you miss even a single tile, even using a screw pump is just going to be pumping stagnant water. 

Plus, once a tile is marked "stagnant", it basically stays stagnant forever, even if fresh water from an entirely new source is poured into dry tiles - and that stagnancy will spread backwards to infect the whole water source, as well.

[Sphalerite]

A problem with using the flow tag to make water not stagnant would be that detection of flowing water in DF is really not very reliable.  As many designs for dwarven water generators have shown, it is possible for a completely sealed body of water to still be considered to be flowing by the game engine.  Just having some of the water at a different depth could be enough to trigger the flow tag and make a murky pool no longer stagnant.

[wierd]

You have to completely replace all walls and floors with constructed walls and floors before water touches them, or else they will be marked as "stagnant" tiles permanently if you are using a screw pump, so if you miss even a single tile, even using a screw pump is just going to be pumping stagnant water. 

Plus, once a tile is marked "stagnant", it basically stays stagnant forever, even if fresh water from an entirely new source is poured into dry tiles - and that stagnancy will spread backwards to infect the whole water source, as well.

This is a problem with "stagnant" and "flow" being non-exclusive, which linguistically they are. Its an implementation problem.  Having flow hard-kill stagnation would solve the problem, as flow over the stagnant marked tile would kill the stagnant mark.

Sphalerites poignant observation that not "level" pools of a uniform fullness (moving depth tiles) would trigger the flow flag, and thus "clean" the pool is a problem of note, but also not far from reality either.  This is exactly what keeps freshwater lakes from being stagnant; wind makes waves, which stirs the water up, and keeps it moving. However, a murky pool simply isn't big enough for wind to be a reasonable explanation for flow, unless the wind is galeforce typhoon-like outside. 

Perhaps a threshold on flow? Greater than 3 depth units per cycle tick?

[CodexDraco]

The stagnant flag could be applied to the water itself instead of the tile it's in. So the flowing single water "block" would be cleaned but the rest would be left stagnant.

[rtg593]

Can a site have both stagnant and salty water?  My current oceanside fortress has several murky pools, none of which seem to be stagnant.  They're probably all salty instead.

Yup. My oceanside embark had a fresh water river and stagnant pools. I connected a pool, river started to become stagnant. I ran an ocean breached tunnel underground and opened it up under that spot, and it started spreading as stagnant salt water.

You have to completely replace all walls and floors with constructed walls and floors before water touches them, or else they will be marked as "stagnant" tiles permanently if you are using a screw pump, so if you miss even a single tile, even using a screw pump is just going to be pumping stagnant water. 

Plus, once a tile is marked "stagnant", it basically stays stagnant forever, even if fresh water from an entirely new source is poured into dry tiles - and that stagnancy will spread backwards to infect the whole water source, as well.

BZZZZ. As long as the water coming out isn't touching the same tile as a stagnant water tile, it will be fresh. Not construction needed.

I just did this on my previous fort to gain water for a well without having to breach the caverns right off the bat.

[wierd]

The problem there is that it looks like stagnant and salty are being treated similarly.

Flows of saline water are perfectly normal and natural, while flows of "stagnant" water are literally impossible.

Because the game needs to remember that an ocean is salty, it can't let the player magically clean it all up using screwpumps and clever archetecture to eradicate all the salt. That's why it marks the container tile.

The problem here is treating stagnacy the same as salinity. They are not the same thing. Agitating stagnant water will actually promote improvements in water quality, even without filtration. The agitation introduces oxygen and other atmospheric radicals into the water which break down the festering microbial goop in the stagnant water, eliminating it from the water as co2, and solid precipitates which nucleate and settle, despite the agitation. (See eg, "river silt").

Thought experiment:

Fishtank. Week with lunged fish (say, mudpuppies, a beta, whatever) in a tank away from home. The filter/bubbler fails.

What does the tank look like when you get back?  Does the filter pack in the filter really retard all the funk growing, or is it just the water moving?