It's often said that finding a source of clean water in a survival setting is a difficult task. While that's sometimes true, it also becomes much easier when you know where to look. There are water sources all around us—they're called plants.
In addition to cleaning our air by transforming carbon dioxide into oxygen, plants suck up moisture from the underground water table and “exhale” it through a process called transpiration. The leaves of trees, bushes, ferns, and other green plants are covered in tiny pores called stoma, which emit water vapor each day during the photosynthesis process. In fact, according to the U.S. Geological Survey, 10 percent of the moisture in earth's atmosphere is a result of plant transpiration. That's a whole lot of water.
We also know that as water passes through a plant, the cells in the stem naturally filter out contaminants like bacteria. So, as long as the stems and leaves of the plant are clean and free of insects, dirt, animal droppings, or poisonous/toxic sap, the water produced by transpiration should also be clean and drinkable.
Sounds good, right? It's clean water, it's produced naturally every day, and it's all around us in the majority of geographic locations. You just need to know how to trap it. This requires the use of a transpiration bag, also known as a clear plastic trash bag. This bag must be placed around a leafy branch, ideally in direct sunlight, and sealed tightly with cordage. Over the course of the day, it will collect water vapor, which will condense onto the inside of the bag, and run down to form a puddle at its lowest point.
Here's a video that shows how to set up a transpiration bag:
If you set up several of these bags, you can capture liters of water without lifting a finger or leaving your camp. So, if you haven't already considered it, you may want to add a few clear trash bags to your bug-out bag or survival kit. They serve many other purposes, including rain shelter and food storage— you can also use them to build a solar still water collection device.