A Water Sieve can turn polluted water into clean water. I discovered my main water source had germs in it, however! How can it be cleaned?


Having played ONI for much longer now than when I originally asked this question, I'd add that prevention is the best solution. Check every few cycles whether your water is clean. If you find that your main (clean) water source has been polluted, reload your save file to a point when it wasn't. Germy, "clean" water CAN be fixed, as described below, but it takes more effort to sanitize the water than to build a base that avoids this problem.

5 Answers 5


I've done a little bit of experimentation with this and mmatthews is correct that a Liquid Tepidizer will kill the germs with heat, however germs will die at temperatures as low as 30 degC, perhaps even lower (this will of course take a long time), my first cleaning system used a tepidizer in line with a Thermo Sensor in order to keep the temperature around 55 degC which was fast enough, higher temperatures ended up damaging my pump (made of copper) with overheat damage.

Note that in the case of slimelung you need to cool the liquid instead.

Chlorine will also kill germs present in air, I'm not sure however if liquids with a Chlorine atmosphere will kill germs in the liquid.


Heat (much like real life) will kill germs. The Liquid Tepidizer building from the Liquid Tuning research can be used to heat a body of water up.

The wiki says that 75 degrees is the upper limit for Food Poisoning germs, but I believe they will start dying as you heat the water up past 50 degrees or so.

  • Heat kills food poisoning germs, but not Slimelung!
    – jvriesem
    Sep 12, 2018 at 16:55

I have found that using a liquid tepidizer along with a pump (gold amalgam) and a germ sensor directly contriving two valves, which is saying that if the water has germs, then the first valve will shut off, having the water cycle through until it is rid of germs.


Chlorine CAN purify literally tons water in less than a cycle!

You need to use a liquid reservoir, a more recent addition to the game. This interacts with its gaseous environment, including the antiseptic properties of Chlorine gas.

First, set up a flow of polluted water or sieved toilet water (or water that's been vomited or urinated into) into a liquid reservoir.

Once you've got a flow into the reservoir, use automated or manual liquid valves (preferably liquid shutoff) to stop the flow of infected water into the reservoir once it's slightly filled. This will give the germs time to die before more is added into the system.

From here, there will be germs in the small amount of piping coming off of the reservoir and into the liquid shutoff. This is unavoidable, as pipes do not interact with Chlorine to purify their contents. Attach a germ sensor within this loop, into another liquid shutoff. If any germs are detected, send the cleaned water one direction. If not, override the liquid shutoff and send them back into the purifying loop for the next round. From here, all dirty water is free of germs. I recommend doing even a third shutoff germ detection, to get any excess from pipes out of the output, just in case any slipped by the germ sensor filtering.

This whole process can be easily automated by timing it with a daylight cycle sensor. The chlorine room is relatively easy to set up, and can take a full input of 2 sieves, easily processing the entirety of waste water from a colony of 32 in a 6x4 or 8x4 tile room.

Although this sounds complicated, it's much easier to set up than a tepidizer, much more power-efficient, and it produces no heat or waste product outside of the sieve.

  • can u make a screenshot of your setup? Jan 31, 2019 at 9:32

The issue with the liquid tepidizer is you also have to deal with the the waste heat, if you do go down that path you can use a liquid seive to drop the temperature to 40c. If you then need to run this through your main inhabited area it will require thought to prevent the waste heat from becoming an issue,even more so if occurring or passing near your mealworm farms.

An alternative is to use a cold biome. Both slime lung and food poisoning die off at 0c so making a "ununununu" pipe radiator snake around a cold biome will drop the temperature to well below freezing even with basic sandstone pipes, if you then store the liquid in a reservoir there you end up with germ free water. I prefer doing this early game as there are more ways to use waste heat from batteries and other core processes to heat the water up if I need it than there are wheeze warts for cooling hot water down.

Also worth mentioning water and particularly polluted water make fantastic heat exchangers in their own right - P-water boils at 120c meaning it can absorb 1/5 more heat before vapourising. I have a game currently where I am keeping a closed room with 2 coal generators at 27c simply by using a a P-water radiator to passively leach the heat out for the price of a liquid pump.

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