Filtering water in order to make it potable is not a complex process. You can easily build your own if you are stuck in a situation where access to pure water is not available. All you need is a thick plastic bag and some basic material, and you can create an effective and practical filtration device that can reduce the chances of ingesting harmful organisms or toxins.
Basic Water Filtration Principles
Filtering water is not magic, it’s science, and very simple science at that. Water flows through large particles such as pebbles or gravel before traveling through layers of finer material. As it works its way through, the filtration ingredients trap particles that are in the water. A carbon layer acts as a microscopic filter that traps microbes and other items that are too small for sand or rocks to capture.
When making a basic filter, you are just arranging the ingredients in their proper order to remove contaminants from the water before it flows out the bottom.
You will need a heavy-duty plastic bag, but don’t worry if it has a hole in it. It needs to be strong enough to withstand the weight of rocks, sand and charcoal in addition to the water that’s being poured through it as well. Ideally, you should also have some string, wire or twine that you can use to hang the bag from somewhere and allow the water to drip through the filter. The easiest way to do this is to tie the top ends of the bag to the cord or wire and loop it over a branch or hook.
Leave the hole in the bottom of the bag if there is one, otherwise poke a few small holes to create a place for the filtered water to drain. You want to make sure that the holes are not big enough for the sand or charcoal to pour through. You can also tie off the bottom of the bag with some string if you have a large hole that needs to be smaller.
Adding the Material
We need to load the filter from the bottom up. You want to have equal parts of coarsely ground charcoal, sand, gravel or small stones, more sand and larger rocks. The thickness of the layers will depend on the length of the bag. Smash the charcoal into a mixture of powder and small nuggets and place it into the bag. Cup the bottom of the bag with your hand and press down on the charcoal to pack it in as tight as possible without breaking the bag. Gently release. Add the layer of sand in the same fashion, holding the bottom of the bag with your hand. Add the gravel without packing it, then add another layer of sand before finally placing the final layer of small stones.
This will be heavy, so again make sure that the bag you chose is heavy enough to hold the weight once it’s suspended and full of water. All you need to do now is to place water into the filter, hang the bag and collect the filtered product as it drips out from the bottom. Keep in mind that you will have to continually add small amounts of water throughout the process because it takes time for it to seep through and out the other end.
This filter can be reused numerous times as long as water is passing through the system. Replace the ingredients once clogs begin to occur. Also, this will remove the vast majority of impurities from the water, but there is always a chance that some microbes get through. Use this as a last-resort when you don’t have access to purification tablets.