This small server-side-only mod turns a button into a working fire sprinkler. Place a button on the underside of a block that is waterlogged (or is a water source), and any fire that starts in the spray cone beneath it is put out just like rain — with a hiss and steam — and burning mobs walking through are extinguished too.

Usage

Place a block and make it a water supply: either waterlog it (e.g. a waterlogged slab, stairs, fence, grate, leaves) or put water above it﹡
Place a button on the underside of that block, so the button hangs from the ceiling. (Any button type works.)

That's it. The sprinkler is now armed. It stays invisible and inert until a fire actually starts (or a burning mob wanders) within its spray cone, at which point it "rains" on just that spot — putting the fire out with the vanilla fire-extinguish hiss and a puff of steam.

Because it is fire-triggered, an armed sprinkler does not hydrate farmland, drip from leaves, fill cauldrons, or boost fishing the way standing rain would. It only acts when there is something to put out.

﹡: actually you can put the water above the solid block above that instead, ie. two solid blocks above the button, with water above those. That way, client-side water drips can be avoided without resorting to using glass blocks. So, a tidy solution is a waterlogged grate or leaf block, above two stone blocks, above a button.

If you don't mind the visual drips, it can just be one stone block between, or even just a waterlogged grate with a button. Mangrove roots and copper grates are good for this because unlike most other waterlogged blocks like slabs, they'll contain the water without flooding, and unlike leaves, buttons can be placed under them.

The spray cone

The spray widens as it falls, like a real sprinkler head, then is confined to an 11x11 square.

The spray falls straight down: a fire is only reached if there is no solid "floor" directly above it, up to the sprinkler's level. A floor is anything that stops falling water the way a roof stops rain — full blocks, slabs, stairs, fences, closed trapdoors. Open trapdoors, string, torches, carpets, flowers, and water/waterlogged blocks all let the spray through.

Fire Sprinkler