I used to have a door as the only break for water and never had problems with trolls. I think it's mostly the rare amphibious titan you'd need to worry about.
Trolls will go for the quickest route into your fortress and your reservoir didn't count for this. Otherwise, I'm pretty sure amphibious creatures will properly consider water tiles when pathing. However, super-secure reservoirs are typically only an issue in evil biomes or when in range of a necromancer tower. Even so, if that rare swimming titan shows up he can and will smash through your reservoir.
I never leave my reservoirs open though. I let in water to fill it up then flip a bridge switch to close it off. If I need more water I just open up the bridge momentarily. In Dwarf fortress, it never hurts to be too prepared, and a bridge is both easy and effective.
I prefer aquifers as a water source. So many people hate them, but they aren't so bad to pierce. Nothing will spawn in your aquifer either, so they start secured. No need to worry about fortifications and bars and bridges. Baring an aquifer, you can siphon off water from a nearby river or build a giant cistern to the side of an underground lake. You can also drain from murky pools- just be sure not to actually destroy any of the murky pool tiles. They have special coding that lets them flood when it rains, otherwise a hole in the ground stays a hole in hte ground. You can build a channel leading from the pools into a drain that enters your cistern, but there will likely be significant water pressure so mark the areas as restricted traffic and make sure the reservoir won't slosh out/flood fort. Then use a bridge as a cover for said hole (hatches can be smashed). This "stagnant" water can be drunk/used to clean wounds, but will cause unhappy thoughts and lead to higher infection rates. You just need to churn it through a pump first, but like with salt water one tile of it will ruin the whole set. Thus, when using stagnant/salty water you build TWO cisterns. The first is a smaller "collection" zone that holds the "bad" water. Then you build a pump that cleans the water and dumps it into your large reservoir. Since water must be at least 2z levels deep to avoid mud and since water will evaporate if it spreads out too much, its best to make your reservoirs narrow but deep. 100 units of water will evaporate in a 10x10 reservoir, but will still last indefinitely in a 5x5 reservoir that of the same depth. You can make the reservoir 4 tiles deep to allow it to hold the same amount of water while having a lower area to evaporate. Wells will go down any number of z-levels to reach the water, so its not a big deal if the bucket is dropped an additional z-level or two from time to time.
One last concern is drainage. From time to time a dumbass-kid or clumsy dorf will fall into your cistern. Now, their rotting corpses won't poison the supply, but they will still cause unhappy thoughts (or prehaps take your last pick with them for their "swim"). Or maybe you just want to reclaim their stuff, either way you want a way to temporarily drain your cisterns. Thus, before filling one up build a few channels leading to a water sink and put a (lever controlled) hatch over them. Proper sinks are aquifers or the edge of the map (can use the caverns or dig to map edge and smooth/carve fortification to work). Then have a floodgate/locked door/bridge that leads to a stairway/ramp to allow anyone inside to run out as you drain. I like to build an airlock here so that when the first door is opened only a few tiles of water will spill into your fortress. So, when you start filling your aquifer from that pond/river and little Urist McDumbass decides to play in the 2/7 water tiles around your drain... he won't be doomed to drown in your cistern. I know, I know, hes useless, however his father might be a legendary axelord with a short fuse... so just drain the reservoir and fish the kid out.
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Topic: Need help getting water... (Read 9123 times)