Clean water is surprisingly hard to come by in Metal Gear Survive. However it’s one of the most essential items you can carry as drinking it keeps your thirst meter up which prevents death and keeps your stamina cap high.
There are three main ways of acquiring clean water in the game. You need to either obtain it from deep within abandoned bases around the world (they’re usually sitting on desks in bottles), from rainwater tanks, or by crafting a campfire with a hanging pot and creating them there. The latter option is the most convenient and efficient but in order to unlock the ability to create campfires with hanging pots you need to complete the mission where you find the wormhole digger (sometime after you rescue the nurse if I recall).
In the meantime, you’ll have to make due with drinking dirty water. Dirty water can be found in shallow pools throughout the world and is extracted in the shining spot somewhere in the pool. It can also be found in sinks at bases. You’ll also need empty bottles or canteens to hold the water. Dirty water not only doesn’t fill up your thirst meter as much as clean water does but it also has a chance of infecting you. If that happens, then you either have to take an antibacterial drug or build a shelter and sleep for six hours. Antibacterial drugs can be found in bases in the Dust, crafted at a medical workstation by combining antibiotics with tarragon, or received as part of a daily bonus from the supply box. Shelters are created after progressing through the game a bit.
Once you craft the campfire with a hanging pot, you’ll be able to take three bottles of dirty water and turn them into one bottle of clean water. Or you can take either five bottles of dirty water or two bottles of clean water along with one empty canteen to create one canteen of clean water which will fill up your thirst meter even more. You can also take a canteen of clean water and an empty bottle to create a bottle of clean water. Once you craft the basic grilled version of animal meat, you’ll learn how to make a soup out of said animal meat and two bottles of clean water. Not only do soups raise hunger meters more than grilled meats but they also boost your sprint speed.
You’ll be able to create rainwater tanks after your get the wormhole digger along with the campfire with the hanging pot. Like vegetable farms for food, rainwater tanks produce clean water over a period of time as long as they’re tended to by a crew member. You can assign crew members from the AI in the middle of your home base.