How To Use Transpiration Bags To Gather Water In A Survival Situation

Survival Water

Water Collection Using Transpiration Bags

Transpiration is the process in which plant life collects distributes and finally evaporates/dispels moisture from certain parts of the plant in particular the leaves. The surface of a leaf has what is called stomata, which are essentially holes or pores. The stomata open and close mainly to allow the exchange of gases. Essentially, green plants absorb carbon dioxide and expel oxygen. There is a much more technical explanation for this process but this is the process in simplified terms.

The stomata also disperse water into the atmosphere, which can be collected using transpiration bags. The evaporation process is accelerated by using clear plastic bags that surround the leaves. The bag allows thermal radiation to heat the leaves and essentially sweat the moisture from the foliage. The bag’s surface allows the collection and entrapment of the moisture instead of having it diffused into the air.

Transpiration bags work similar to a solar distiller, but with considerably less effort, which means you are not using more sweat than what you can collect in water. In a survival situation, you have to weigh the effort against the results. A solar still usually requires considerable digging. You need a shovel/entrenching tool, a sheet of plastic and a collection cup and adequate ground moisture.


Materials Needed To Take Advantage of the Transpiration Process

  • Clear plastic bags, they should be clear to allow the sun’s rays to penetrate. The leaves absorb sunlight, which triggers photosynthesis, which in turn causes the stomata to open allowing for faster evaporation of the moisture in the leaves
  • Cordage used to seal the bag tightly around the foliage
  • Filtration material such as a bandana, article/piece of clothing or coffee filters
  • Collection container, such as a canteen, canteen cup or suitable metal container
  • Small weight such as a rock that is placed inside the bag

Evaporated water is purified water. The evaporative process leaves any impurities behind, such as high concentrates of sodium (salt), and other impurities. The foliage itself however will have pollen, dust and possibly insects on it/in it and these contaminates may very well end up in the water if they are trapped inside the bag. It is recommended that you have the means to filter the water. The water will not require purification. However, it is important that you do not use a transpiration bag on any poisonous plants or foliage. Use easily identifiable trees, such as oak, maple, birch and so forth. Pine trees are not ideal for water collection using this method.

The bigger the bag (surface area) the greater volume of water you can collect. The bag must be filled as full as possible with the foliage without puncturing holes in the bag. Of course do not cut the limbs/foliage from the tree; the bags must be placed on live undamaged limbs.

Find a well-developed tree, and before enclosing as much of the foliage as possible, place a small rock in the bag. Once enclosed tie the bag around the limb tightly, you want to make it as air tight as possible. Jostle the bag until the stone is in one corner of the bag. The moisture will condense on the inside of the bag and begin to flow toward the depression made by the rock.

Allow the water to collect in the depression and when you are ready to collect the water have your collection vessel ready with the filtering material over the mouth of it. Put a small hole in the bag where the water has collected and let drain through the filter. When empty tie off the end with the hole in it, jostle the rock until it is in another part of the bag, and repeat the procedure. Do not leave the bag on the limb longer than three days. Below is a good video I found that will show you the process.