Everyone knows that boiling clear water will sterilize it and make it safe for drinking. If the water is dirty/cloudy you need to filter the water first. Pouring the water through a folded up t-shirt works well. You want to get your water as clear as possible.
The questions is, how do you boil water if you don’t have a metal cup or pan? This video answers that question whilst also teaching you two great bush-craft/survival techniques: how to boil water with hot rocks and how to make a cup/bowl from willow bark. Combine the two techniques and you can boil water in the wild.
This video shows the wrong way to boil water. There should be two containers. When you heat up the rocks, you fist dip them in one container filled with water to WASH the rocks (quickly) and then drop them in the second container to actually boil the water. This will save you 1) eating/drinking the charcoal/ash on the rocks and 2) charcoal is carcinogenic. Plus the water will be filthy. The first dip in water works really well especially if you quickly dip them in the water still holding on with tongs and then drop it in the second.