Water is the biggest necessity on an outdoor trip. And, if you run out of it in an emergency situation where you are waiting on rescuers, you probably will begin praying for rain. The easiest way to collect precious rainwater is to catch it as it falls out of the sky. It is the cleanest most drinkable that you can get in the great outdoors, way better than possibly bacteria-filled water from lakes and streams. But, sometimes you may find yourself in a survivalist situation where it had already rained, and you missed it as it was falling out of the clouds.
If you didn’t think to collect any while it was raining you are now regretting it as you look into your backpack and notice that your bottles are getting really low. But you may not be completely out of luck. After a good rainfall, everything around you is still wet. You’ll probably look around and see a big wet patch of moss for example. You could take that and ring it out into a container to transfer to your water bottle or canteen. All the leaves around you are also very damp, and you could do the same thing as you did with the moss to extract water from them by hand.
You could possibly end up with a liter or two in about an hour or so. In severe survival situations, though, you’d have to take things to another level to collect precious, automatically drinkable rainwater. Find some tall grass or lots of huge leaves to walk through, and purposefully soak your clothes with the rainwater. Then, you simply ring your clothes out into a container. Rain water doesn’t have to be purified, so if you can collect enough of it you’ll save a lot of purification tablets for when you really need them.