The Complete Beginner's Completely Incomplete Guide to Oxygen Not Included


  • You can see the Plumbing Overlay by clicking on the water drops in the top right or by pressing F6.

  • You build most plumbing-related stuff through the Plumbing build icon (bottom left). A notable exception is the sink, which is found under Medicine.

  • Plumbing things commonly have an input and an output.

    • White is input: liquid goes in here

    • Green is output: liquid comes out here

  • If something isn't working, the first things to check are the inputs and outputs. A common mistake (even after thousands of hours I still do it) is connecting inputs or outputs wrong.

  • A pipe must lead somewhere for liquid to flow along it. (A Liquid Bridge counts as somewhere - water will flow up to the start of the liquid bridge, even if the pipe goes nowhere after it.)

  • If you want liquid to pour out of a pipe, you need to put a Liquid Vent at the end.

  • Gravity affects liquids on the map, it does not affect liquid in pipes.

Tip reminder: plumbing basics



There are many variations of "use chlorine to kill germs" -builds. This particular build I picked up from a YouTube video by Francis John.

Source: "QOL Mk3, 36 Germ decontamination for toilets and spin that vacillator : Oxygen not included", by Francis John. Available at:, accessed 11 August, 2020.


The goal is to take the polluted, germy water from our bathrooms and turn it into clean, germ-free water. And then feed it back to our bathrooms.


Such a water recycling build isn't difficult to put together, it just requires a bit of attention to detail when building.


The challenges and solutions

When we run polluted water through a Water Sieve it turns into water. Since bathroom and shower inputs need water, and we would have just created water, we could then simply feed that water back into our bathrooms and showers. However:


  • a Water Sieve will not remove germs from water.


So we would end up with germ-infested water used as clean water in our bathrooms and showers. (Germs in water aren't visible. To see germs, use the Germ Overlay.)


To solve this issue, this build uses chlorine.


  • Chlorine kills germs

We will send all germy water through a room full of chlorine to de-germify (that's definitely a word) it.

Note: We could also kill the germs by heating up the water (to 60ish degrees, last time I tried it at least). But that would require power - and then cooling the water back down would require even more power. I used to do this. I can't remember why, but I imagine it was because I wasn't sure how chlorine worked. Don't do what I did - go straight for a chlorine build.


The quick & dirty (read: germy) version

At the time of writing, germs in the clean water of showers and sinks don't spread to dupes. So while carrying, say, germy dirt will make dupes germy, showering in germy water will leave them germ-free.


I don't know if this is a bug or a feature - if it will be changed in the future or stay this way. But since it has remained this way through both the launch of the game and the DLC, I'd imagine it will remain.

The idea of becoming germ-free from washing your hands with germ-infested water is immersion-breaking for me, so I don't do it. But if you don't suffer from the same hangups as I do, this mechanic means that you can actually skip the de-germing part of this build (the chlorine room). Which will make this build both quicker and easier.


The liquid overflow mechanism


Regardless of whether you include the chlorine room in your build, there is something important to remember when recycling bathroom water:


  • Toilets produce more liquid than they use

Toilets produce more polluted water than they use water. This means that if we build a closed loop - polluted water is sent through a Water Sieve and fed straight back into our bathrooms - then the pipes will eventually fill up and clog. This wouldn't break the pipes, but it would cause our bathrooms to stop working since there would be no room for new polluted water in our pipes - no room to flush the toilet, basically


We can solve this problem by including a way for excess water to be dumped out of our plumbing network. This is done using a bit of piping called a Liquid Bridge.

Something useful to know about Liquid Bridges:


  • There is never any liquid in a liquid bridge. It teleports liquid from the input pipe to the output pipe. Meaning:

  • You can deconstruct Liquid Bridges without any water spilling out

(As a bit of an aside, this is a useful feature to use when you want to have the option of expanding a pipe network later, like for instance extending a cooling loop. Put a liquid bridge where you might want to change the piping later. Then you can delete the bridge and change the piping without causing a mess.)


The Liquid Bridge has an input side (white) and an output side (green). One of the uses for a Liquid Bridge is to be able to run entirely separate pipes underneath it. Another use is to create that liquid overflow mechanism we need.

The way liquids work in Oxygen Not Included is that liquids "prefer" liquid bridges over other pipes. If a liquid comes to a point in a plumbing network where there is a liquid bridge and a normal pipe, the liquid will always first try to use the liquid bridge. Only if that isn't possible will it flow into the normal pipe.


Liquid overflow mechanism using a Liquid Bridge. Liquid always first tries to cross over a liquid bridge. In this design, that means the top tank would fill first, and only then would the bottom tank start filling up.

This is probably easier to understand as an image. In the picture this "liquids prefer liquid bridges" -thing has been used to create a main storage tank and a secondary storage tank. The water being pumped will first try to pass over the bridge to the top tank. Only when both the tank and all the piping after the liquid bridge are full will the second tank start filling.

This is the mechanism we will use for our bathrooms - ensuring that our bathroom loop will have as much water as it needs, but any excess will be gotten rid of.


The build

Regarding the order of things: if we send the polluted water through the water sieve first, then the water sieve will produce germy dirt. If we get rid of the germs in the polluted water first, then the water sieve will produce germ-free dirt (as long as we don't use germy sand in the water sieve).

  • So we will first kill the germs in the polluted water, then run it through a water sieve

Then there is the issue of where to put the liquid overflow mechanism. Where to put it depends on whether we want to have a small, steady supply of polluted water or of water as our overflow.

If the liquid overflow mechanism is before the cleaning process, we get germy, polluted water as overflow. If the liquid overflow is after the cleaning process, we get germ-free water as overflow.

  • Polluted water as overflow can be used to feed a thimble reed, giving you a bit of reed fiber as a byproduct.

  • Water as overflow can (for instance) be used to feed your SPOM and generate oxygen.


The building of the build

For the most part, this is a straightforward build. There is some piping that needs to be done just right and a tiny bit of automation. We will also need to create a vacuum and then fill that vacuum with chlorine. But none of it is actually that difficult. The main tricky part of building this has to do with how chlorine works.

  • Chlorine kills germs in liquid reservoirs

  • Chlorine does not kill germs in liquid pipes

Our build will use a room full of chlorine that our germy water will spend enough time in that all germs are gone when it comes out the other end. To make sure it stays in chlorine long enough, we will use four liquid reservoir tanks.

(Note: You only need three liquid reservoir tanks. For the longest time I was worried that three wasn't enough. But since writing this section I have switched to using three tanks and haven't had any problems. )

If we were to just build everything and then start the build, the germy water would still be germy when it came out the other end. This is because the germs in the polluted water in the pipes wouldn't be affected by the chlorine.

There are two ways you can solve this:

  1. Fill your chlorine room tanks and pipes with germ-free polluted water. You can find germ-free polluted water in the slime biome.

  2. Construct the build using toilet water, but do it in two stages. Fill the tanks and then let them sit in chlorine until the water is germ-free. Then delete pipes with germy polluted water and re-connect your reservoirs, then start your system.

Option 1.

The first option - filling your liquid reservoirs with germ-free polluted water from the slime biome - is cleaner and easier. It is the approach I recommend, and the approach I take when on a map with a slime biome (as they have germ-free polluted water - use the germ overlay to check).

You bascially just build the whole thing without needing to do any of the deconstructing in method 2. When it's all built and the liquid reservoirs are full, you "plug in" your bathroom (etc.) water outputs to your decontamination system. (There are several pictures of the build below.)

Option 2.

The second method is a bit more complicated, so I'll cover it here. This build will involve some deconstructing of pipes and some cleaning up of polluted water.


The benefits to this approach is that you don't need germ-free polluted water for it, and that you can hook up your bathrooms (etc.) to it right away.


Stage 1: feeding our polluted water to liquid reservoir tanks

In the picture below, I have combined all my polluted water producing buildings in one area. All of which feed their polluted water to four liquid reservoir tanks at the bottom. That area will become the chlorine room. (And to the right of it we'll put in a water sieve.)

The piping connecting the four reservoir tanks is temporary and will be deconstructed when they are full.


Step 1: The basics in place. I have built all the stuff I will want to have hooked up to the water recycling. From the top: (an incomplete) Hospital with functioning toilet and sink, showers, bathrooms, and a dumping station for polluted water bottles + compost and sinks to wash hands when leaving the room (the door on the left is enter-only). On the bottom are my four reservoir tanks slowly filling up with polluted water. There is an overflow mechanism that feeds to a tank and a Reed Fiber plant (see the liquid overview below).


Step 1: Liquid overview. A pipe overview of the same build. When finished, the clean water will come from the soon-to-be-built chlorine room on the bottom floor. It will pass through a water sieve (not built yet) and feed back into the clean water input pipe.


Close-up of liquid overflow mechanism (mid-left). Polluted water wants to flow over the Liquid Bridge, from white to green. If it can't - if the pipe on the other side of the Liquid Bridge is full - it will flow into the Liquid Reservoir instead.

The liquid overflow mechanism feeds a Thimble Reed plant. This design includes a liquid reservoir tank for the liquid overflow. This isn't necessary - you can also just have enough Thimble Reed plants to take care of all the water. However, there are some benefits to a tank.


The main one being it will give you some leeway if something goes wrong with the Thimble Reed. What could possibly go wrong with it, I hear you ask. Well, I can tell you - from personal experience. (There is no better way to learn Oxygen Not Included than to screw things up.)

Thimble Reed only grows in a specific temperature range, between +22 and +37 C. If you ever dump cold polluted water into your system (melted polluted ice, for instance), then the Thimble Reed will stop growing. And your system will start backing up until the water is sufficiently warm. (If that happens, you can use a Space Heater as a quick fix.) If you don't have a polluted water bottle emptier connected to this system, then the only problem would be if that area of your base became too hot or cold for for the thimble reed.

/Addendum: "new" food mechanics. After writing this part of the guide, this actually happened to me - the whole room went too hot for thimble reed to grow. Because of the composts. If you have a lot of food going bad - as can happen with the way food spoils in new updates of the game - then your composts might be in very active use.


If this becomes a problem you can either move the Thimble Reed somewhere cooler or implement some cooling in the room. (We'll cover cooling loops later.)


Another option is to switch to having clean water overflow that you feed to your SPOM, rather than polluted water overflow. And yet another option, this one for decreasing the amount of food that goes bad, is to switch to Berry Sludge. (It is made from Bristle Blossoms and Sleet Wheat.) This will help because Berry Sludge never spoils. Now back to the build./

Once you have your (three or) four reservoir tanks filling up, you can start building your chlorine room around them. The first step is creating a vacuum.


Stage 2: Building a vacuum room

We want a room full of chlorine. If our room were to have a lot of chlorine, but also a small of amount of some other gas, then we wouldn't know for sure if the germy polluted water will spend enough time in chlorine to kill all the germs. So we want only chlorine in our chlorine room.

To do this, we will have to build a room and then empty it of all gases - create a vacuum. But we also want to be able to access the room once it's a vacuum. To accomplish this, we will need something called a liquid lock. A liquid lock lets dupes pass through, but not gases. Then we pump out all the gases in the room and finally we fill the room with chlorine.

(Note: here I'll show you how to build a proper liquid lock. When you have the hang of them, and if you're feeling lazy, you can start building half-assed, quicker-but-riskier versions. Covered in the section on liquid locks.)


Building a liquid lock, part 1. Build  the left wall and build the bowl/stairway-like thing in the picture. Set the bottle emptiers to Water, then click Enable Auto-Bottle.


Building a liquid lock, part 2. Once there is water in the second layer, set the bottle emptiers to no longer accept any liquids. (How much water? I once saw someone - I forgot who, sorry - recommend using roughly 300kg in each tile as a target, and that has worked fine for me.) Then build the final upper tile.


Building a liquid lock, part 3. In Oxygen Not Included, a tile cannot contain both a liquid and a gas. This means that, when built, the final upper tile will "pull" the water up to the bottom of it. Now gases cannot pass through - our liquid lock is complete.


Pump out all the gases. Build a gas pump with a gas pipe that leads out of the chlorine room and empties out through a Gas Vent. (Or a High-Pressure Gas Vent if you have plastic.) The gas vent will not allow gases to exit if the gas pressure is above 2000 g. If that becomes a problem, you can build a long gas pipe with several Gas Vents along it.

Stage 3: When the tanks are full, delete the pipes & mop up


Don't deconstruct the pipe in the wall. Unless it's safe for polluted water to spill out the left and into your base. (If so, delete away!)

When the liquid reservoirs are full, you can delete the temporary pipes. (This can be done before or after building the airlock and pumping out the oxygen - it doesn't matter which.) First:


  • Double-check that your liquid reservoirs are full

If you have a dupe with the plumbing skill, empty the pipes before deleting them. (Using the "Extract Pipe Contents" icon in the bottom right.)


If you don't have a plumber, you will have to go for the messy option: just delete the pipes, let the polluted water spill out and then mop up the mess.

NOTE: Be careful with the liquid pipe in the wall. If deconstructed, polluted water in the pipe in the wall will spill outside of your vacuum chamber. In the picture on the left, polluted water would spill out on the left side of the wall and pour down the base.

As for deconstructing pipes:

  • An easy way to deconstruct pipes - and only pipes - is to select the Plumbing Overlay and then pres "X". Now you will delete only the pipes.

When done deconstructing, issue a mop command (if necessary) and a sweep command to get all the bottles of polluted water out of the room. Polluted water bottles can emit polluted oxygen, which we don't want in our chlorine room. (Dupes will only sweep polluted water bottles if there is a bottle emptier somewhere that is set to accept polluted water. If you don't have one as part of your bathroom build, build a temporary one somewhere.)

When the polluted water bottles are gone and the room is a vacuum, you can delete the gas pump. If you want to see your progression towards a vacuum, you can check gas pressure levels using the Materials Overlay (click the square icon in the top right, or F4).

As of some update some time ago (can't remember when), dupes shouldn't exhale carbon dioxide in a room full of nothing (vacuum) or of chlorine. At least that's what I remember reading. (I haven't had problems with vacuum or chlorine rooms getting carbon dioxide from dupes building in them, at least.)

Note: since writing this I have once had carbon dioxide get into a vacuum room. However, I've probably built hundreds of vacuum rooms over the years. I don't know why this has happened once and only once. You can build a safeguard by adding some automation - an on/off switch - to the gas pump. Turn it off when the room is a vacuum, then delete the pump only if (or when) the chlorine room works.

Regarding flatulent dupes. Flatulent dupes are multitaskers: they are perfectly capable of holding their breath in a vacuum while simultaneously distributing natural gas into the room. And thereby  destroying your vacuum chamber. If that happens, curse under your breath and promise to never again take a flatulent dupe. Then start over with the vacuum room. (You can add a door that blocks the dupe from entering using door permissions.)


Clean up the mess, get rid of the polluted water bottles, wait for the gas pump to create a vacuum. Sorry Marie...


Stage 4: Fill the vacuum room with chlorine


Bleach Stone


Storage Bin with Bleach Stone

There are two main ways to get chlorine into the room:


  1. Find chlorine on the map. Then pump it through a gas filter (set to chlorine) and either pump it straight in to your chlorine room or use a canister filler and canister emptier to get it in.

  2. Use Bleach Stone


Bleach stone is probably the more beginner-friendly approach, so we'll use that.

Bleach stone can be found in the caustic biome - the one with a lot of purple.

Once dug up, bleach stone will start emitting (small amounts of) chlorine. So the idea is simply to dig some up and put it in the vacuum chamber. As the bleach stone emits chlorine, the room will turn into our chlorine room.

  • Build a Storage Bin in the room

  • Set it to only accept Bleach Stone - found under Consumable Ore (Note: Bleach stone will only become available as an option when you have dug some up. If it isn't visible, check again after digging some up.)

  • Raise the Storage Bin priority (to 7 or so)

  • Dig up some bleach stone

  • Set a sweep command for the Bleach Stone

Dupes will then move the bleach stone to the storage bin and the room will fill up with a slowly but steadily increasing amount of chlorine.

Some chlorine may get into your base during this process. It's not a big deal. (We can clean it up later.) (Or say we will but then somehow never quite get around to it.)

​How much Bleach Stone should you use?

Currently, the way chlorine works in the game is that any amount of it is as good as lots of it. Meaning, it doesn't matter how much bleach stone you put in the room. So dig up, say, a tile or two. (100 kg is more than enough.)

If you already have bleach stone from earlier excavations, and don't want to use it all here, you can set the storage bin to only accept a smaller amount than the default value.

I used to worry that too much bleach stone would create so much chlorine that the gas pressure could damage the walls. Which, it turns out, is not how bleach stone works - once the pressure reaches a certain point (1800g), it stops emitting chlorine. So as of this writing, you cannot have either too much or too little - any amount of bleach stone is fine.

Once the Bleach Stone is in the Storage Bin, you can delete the Storage Bin. (If you have some other Storage Bin in your base set to Bleach Stone, you will have to temporarily disable it if you don't want your dupes to come remove the Bleach Stone you have here.)


The Materials Overlay. You can use the Materials Overlay (the square icon in the top right) to double-check that you have chlorine - and only chlorine - in your chlorine room.

Once this is done, we wait for the chlorine to work its magic on the germs in our reservoir tanks. Using the Germ Overlay, keep an eye on the tanks. When they are germ-free, we can continue.

Stage 5: completing the chlorine room - pipes and automation

First, the theory behind what we are about to build:

  • Chlorine kills germs in liquid reservoir tanks

  • This happens fairly quickly, but not instantaneously

  • Our entire water recycling system is a big loop

  • We want germy water to pass through the chlorine room slowly enough that all germs die before moving on to the next part of the loop

The way we implement this is through

  • the liquid reservoir tanks we have built, and

  • a neat little bit of automation that makes sure the reservoirs are always full.

So only when polluted water enters the first tank at the beginning of our chlorine room will our setup allow polluted water to exit the last tank of the chlorine room. And only the same amount of polluted water is allowed out as came in, making sure the polluted water reservoir tanks stay full.

This system means germy water spends enough time in the tanks on its way through the build that it will always come out germ-free, even if there is a continuous flow of polluted water into (and out of) the system.

In this build, we will use a Liquid Pipe Element Sensor (unlocked in Liquid Tuning in the Liquids research branch). It allows us to detect what liquid is in a pipe and use that information to send an automation signal.

We will connect it to a Liquid Shutoff. Which is basically an on/off switch for the pipe. Then we will use automation to decide when to let polluted water pass through.


There is one part of the plumbing network that has a lot going on, making it hard to see what is built. I will show that part first. Then some overlays of the entire chlorine room.


The confusing section of the plumbing.

The first two pictures show different parts of the build, the third picture shows what it looks like when done.

Two liquid bridges.

The inputs (the white bits) are on the left, the outputs (the green bits) are on the right.

Two sections of liquid pipe and a Liquid Element Sensor.

There is a liquid pipe section under the Liquid Element Sensor.

The finished version.

This is what the piping and sensor look like when built.

What does this pipe-sensor-thingamabob do? The design uses the same mechanism as the liquid overflow section.


Polluted water coming in (from the bottom left) first tries to cross over the liquid bridge (on the bottom). If it can't - if the tanks are full - it sends the water around the U-turn with the automation sensor. That leads to a second liquid bridge and back to the tank.


When water enters the pipe with the sensor, it sends a signal letting our chlorine room know that it can let out some water.


The next part of the build.


The liquid overlay. All the tanks are connected. The last tank leads to a Liquid Shutoff.


The automation overlay. The Liquid Element Sensor is connected to the Liquid Shutoff. The Sensor is set to Polluted Water.


The power overlay. The Liquid Shutoff needs 10 W of power. Use Conductive Wire if possible to decrease the risk of overload. (We will be walling off the chlorine room next.)

Now we can close off the chlorine room and make space for the Water Sieve. A tiny bit of chlorine will escape into the base. You can avoid this (if you want) by building over the chlorine tiles.


Close off the chlorine room. Continue the wall next to the Liquid Shutoff up to the ceiling. Optional: also build over all chlorine tiles so none escapes into your base.

Then delete the remains of the liquid lock, leaving only the wall to the chlorine room. (Let the water pour wherever or pump it out first. We just want to get rid of it - we need the space.)


Stage 6: Adding a water sieve and connecting it all up

Almost done, believe it or not. Now we add a water sieve, power it, and then connect the final pipes.


Water Sieve (and storage bin for sand). The polluted water should feed to the input pipe (the white bit). The output pipe (the green bit) feeds back to your system's clean water supply pipe.


Note: If you want your overflow mechanism to be for clean water rather than polluted, put the liquid bridge after the water sieve output. Between the water sieve and your clean water network. (In this picture above that would be above the storage bin.)


If you have Mechatronics Engineer unlocked... You can add an Auto-Sweeper to feed sand to the water sieve. And a Conveyor Loader to dump polluted dirt by your compost.


Build the final bit of pipe. Connect your bathroom polluted water to your chlorine room. Connect your water sieve output to your clean water (if you didn't do it yet.)

Once the first liquid reservoir tank in the chlorine room fills up (it lost a small amount of polluted water filling up the pipes in the chlorine room) your water reclaiming system will start outputting clean water. You can now disconnect your original water source from this build.

Give yourself a pat on the back - you should never again need to worry about your bathroom water supply.