The water filtration machine in Subnautica is a structure that allows you to transform seawater into large filtered water and salt. At the beginning of the game, the only way to obtain filtered water is by hunting bladderfish and bringing them to the fabricator. However, this is a very tedious task as these small fish are very elusive, making obtaining water quite a challenge. For each fish you catch, you can get a bottle of filtered water, which will restore 20 of your water points.
Another way to obtain water is through bleach. By using one unit of bleach in the fabricator, you can obtain a bottle of disinfected water, which will restore 30 of your water points. To obtain bleach, you need to place one unit of salt and one unit of coral tube sample in the fabricator.
Furthermore, with the salt obtained from the water filtration machine, you can manufacture bleach to obtain disinfected water. You can also use it to preserve food, which will increase the time it can be consumed.
To build the Water Filtration Machine, you first need to research it, and to do that, you must find at least one fragment. These fragments are scattered throughout the map, especially in the wrecks of the Aurora. Once researched, you can construct it in your underwater base using the Habitat Builder, either in a Multipurpose Room, where it fits, or in a Large Room. To build the Water Filtration Machine, you need three units of titanium, one copper wire, and one unit of aerogel.
The Water Filtration Machine produces salt and one Large Filtered Water, which restores a total of 50 water points. If your base is located on the surface, then salt will not be produced as it extracts water from other sources. However, the time it takes to produce water will be much longer than in an underwater base. If we access the purifier menu, we can collect the salt and the water it has produced.
If you have followed all the steps but still can't produce water, it's possible that you are not supplying enough power to the Water Filtration Machine. Keep in mind that this machine consumes a total of 51 units of power per minute, so you will need one or multiple stable power sources to feed it. You can use solar panels if you are near the surface, or other energy sources such as a bioreactor or a thermal plant if you don't have access to sunlight.
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