A sheet of plastic
A tool for digging
You dig out a hole of varying sizes and then secure a sheet of plastic above the hole with rocks. Then you place one rock in the center so the sheet sags down to where you’ve placed the bucket.
Basically the soil is heated by the sunlight passing through the plastic sheet, condensation collects on the plastic sheet and gathers in the bucket. Depending on the day and where you’ve placed it you can probably get a bottle of clean water a day from one.
So it wouldn’t be a complete solution to water needs but I think it would be a nice high end survival recipe that, by the time you can build one and passively gather water, it wouldn’t be game-breaking as much as it would be a convenience.
Make them traps, so if an animal steps in them they stop working. Also, that would be a lot of sheets. And it’s far more trouble to gather from a bunch of squares than sit by the river boiling water at two keystrokes per unit. I think they’d be decently balanced.
Spamming them across the map seems lioe it should take a great deal of effort, I don’t think there’s any need to cut off the reward 8f they go through all that effort, and this isn’t even considering having to go around collecting water across the map.