One of the easiest ways to collect water in emergency situations is the transpiration technique. Using just a clear plastic bag and some type of cordage for tying, you can obtain enough water from the natural cycle of plants to stay alive.
Transpiration is the process of water movement through plants. Plants absorb water through their roots in the soil, then cycle it through their stems and leaves to utilize nutrients. Much of the water is then evaporated into the atmosphere. We can utilize this natural process and gather the water that plants release for use for survival.
Clear plastic bags should be a part of every emergency kit, and are especially useful for this simple survival technique. To use this method to obtain water, start in the morning to make the most use of the daily transpiration cycle of the plant. Take a plastic bag and tie it around the branch of a leafy, non-toxic tree or shrub, bunching as many of the leaves as possible into the bag without tearing it.
Tie the open end of the bag to the branch, keeping it as airtight as possible to prevent water loss.
At the opposite end of the bag, loosely tie off a corner to create a small reservoir. Adjust this corner so it sits lower than the rest of the bag, or put a small rock in the bag to weigh it down. This is where the water will collect, and tying it off loosely will let water pass through while keep leaves and other larger debris out of the collected water.
Throughout the day, as the sun shines on the bag, condensation will form and the water droplets will collect in the reservoir. The water can be collected at the end of the day, when the transpiration cycle is complete. It may retain some of the taste of the foliage, but is clean, potable water that is safe for drinking. Typically, the more sun that shines on the plant during the day, the more water you will be able to collect.
This method will not collect a huge amount of water per day, but can suffice to keep a person alive, and greater amounts can be collected if you have multiple bags to use.