Resource Cycling

Most survival-critical resources in Oxygen is Not Included can be transformed into one another via various processes. This allows for cycling between desired outputs, often just using basic inputs such as a Geyser output. This idea is the foundation of sustainable base building. It is often difficult for new players to identify successful cycles, which in turn makes it difficult for them to produce sustainable bases.

## Water Cycling

Water is the backbone of sustainability. It is the primary long-term source of Oxygen & Calories for sustainable bases, and can also serve as a key source of Power. Water can also serve as an indirect source of Slime & Dirt, and is a core component of Steam loops used to generate cooling or power.

* **Oxygen**. There are two paths that Water can take to become Oxygen and a third that requires Rust. The first is the direct off-gassing of Polluted Water into Polluted Oxygen, a key source in the early game which requires Deodorizers but no heavy machinery. The second is the production of clean Oxygen & Hydrogen from Electrolyzers. This requires more machinery to be consistent and to account for the high temperature of the resultant gas. Electrolyzers serve as the backbone of a Self-Powering Oxygen Machine (SPOM) and will be a major part of any long-term base. Finally, Oxygen can also be produced from Salt Water by filtering out the Salt and combining it with Rust in a Rust Deoxidizer.
* **Calories**. A wide variety of crops take in clean Water to grow, and several take up Polluted Water (most notably the new Bog Bucket from the Spaced Out DLC). Lettuce is the lone plant that uptakes Salt Water. Crops tend to have fairly specific temperature requirements, although they can technically take inputs of any temperature. An out of temp liquid input will eventually normalize with the tile into which it is being pumped, but it should not be seen as a major disaster to have a couple of 30°C packets of Water heading into a Bristle Blossom farm.
* **Power**. Water can be converted into Power in two ways, one associated with Oxygen production the other serving as a heat sink. Electrolyzers uptake Water and output Oxygen & Hydrogen. The amount of Hydrogen an Electrolyzer produces can be converted into more Power than it takes to pump the Water into the Electrolyzer, run the Electrolyzer, and vent the output gases. This system can be optimized in a variety of different ways and is the relationship that makes SPOMs self-powered. Water boils into Steam at around 100°C (slightly higher for Polluted Water & Salt Water). Steam of 125°C to 250°C can be fed into a Steam Turbine to produce power. This process deletes most of the heat, outputting warm Water from the Turbine. This is an extremely effective late-game source of power as well as the primary source of cooling for most bases. Steam looping requires Water, but it doesn't change the total mass of Water/Steam in any way and can thus be a closed loop.
* **Other Resources**. The most obvious additional resource that may require Water is Reed Fiber, grown by feeding Thimble Reeds Polluted Water (or by shearing Dreckos, which can be done sustainably without using any resources via Balm Lilies). Bathroom loops produce slightly more Polluted Water than they intake clean, and a single Thimble Reed serves as an excellent sink which keeps the system balanced (just make sure to use Liquid Bridges to maintain priority to the Toilets!). Polluted Water can also be used to produce Polluted Oxygen, which can in turn be converted into Slime by Pufts. This relationship also has the pleasant outcome of preventing the Slime from losing mass as it sits in the Polluted Water. Slime can be used to produce Algae, used to produce Calories by fertilizing Mushrooms, or cooked into Dirt. Dirt is also a byproduct of sieving Polluted Water into clean Water, although the Puft -> Slime route provides a better conversion ratio. Salt can be boiled out of Salt Water or Brine, or more efficiently produced with a Desalinator.

## Mineral & Dirt Cycling

Most of the mass of an asteroid is usually in the form of some combination of Minerals, such as Sandstone, Granite, or Igneous Rock. As a base is made up of empty spaces filled with gas not solid blocks of rock, there is invariably a large excess of Minerals produced over the course of the game. While not immediately renewable, Magma from a Volcano or Regolith from Meteors serve as renewable sources of Mineral mass. Additionally, any system which produces Polluted Water can serve as a source of Dirt or Sand.

* **Coal & Calories**. Hatches & Stone Hatches consume most Minerals and output Coal & Calories (in the form of eggs & meat). Hatches are typically the first critter a player will encounter in a normal playthrough, and are extremely easy to ranch. Sage Hatches serve as an upgraded source of Coal, converting 100% of consumed mass into Coal (making the Calories produced "free"). However Sage Hatches have a specific diet of biomass, and are thus most often fed off Dirt (it is possible to feed them off food directly, but this is generally considered a suboptimal choice. You are trading Calories for Coal at that point, and in general other forms of power are much more efficient or easy to manage. Manual Generators offer the same trade for example, but scale with dupe skill, are super cheap, and require no specialized morale investment). Stone Hatches have the additional advantage of being able to mutate Smooth Hatches. Smooth Hatches offer a low-efficiency way to convert Metal Ore into Refined Metal, albeit one which requires no power and produces no extra heat. Smooth Hatches are thus caught in the awkward space between no Refined Metal and a Metal Refinery, with most players preferring to only use Hatches to produce Coal. Once Space is reached, Shove Voles become an option. Shove Voles consume Regolith & Sand (which in turn means they can consume any Mineral) and produce Calories. Uniquely they have no stable limit making them the defacto late game meat source. Shove Voles also serve as an excellent way to dispose of excess Regolith until Magma melting is established.

* **Sand/Dirt Cycling**. All Minerals can be crushed down into Sand. Sand can then be used to produce Glass, a process that naturally occurs when Sand gets too hot or when using the Glass Forge. Sand can be fed to Hatches, it can be converted to Polluted Dirt with a Sieve, or it can be converted to Clay with a Deodorizer. Clay can be kilned into Ceramic, making Deordorizing an essential process on makes with little or no naturally occurring Clay. Polluted Dirt can be fed to Pokeshells (who also produce Sand), composted back into Dirt, or offgased as a source of Polluted Oxygen (which can in turn be used to produce Slime as outlined above). Sand thus serves as an important middle-step material which connects bio-processing (involving Water, Oxygen, and Dirt) with mineral processing (involving rock, Metal, and Coal).
* **Magma**. Later on in the game Magma becomes an attractive source of energy. The heat it produces is ideal for Petroleum boiling or Steam Turbines, and can also be used more delicately to convert biomass (such as Dirt or Slime) into Sand and Sand into Glass.
* **Arbor Trees.**

## Petroleum Cycling

* **Basic Refining**.
* **Carbon Dioxide**, aka Slicksters.
* **Petroleum Boiling**.
* **Sour Gas Boiling**.

## Chlorine & Sulphur Cycling

* **Chlorine**.
* **Sulphur**.

## Metal Cycling

* **Ore to Refined**.
* **Ore to Power**.