One of the most enduring images that shows a lack of preparation for emergencies is the too-frequent scene of people standing in floodwaters desperate for the delivery of bottled water. Granted, flood waters are dangerous and they should be your last resort, but they are usable if you have a little knowledge and a little prep.
There are three things that make any water dangerous whether it’s a flooded river or a stagnant pond.
- solid matter – sand, dirt, algae and other debris suspended in the water
- chemicals – in flood waters the most common danger is oil and gas that’s coming off flooded streets or out of storage containers
- pathogens – bacteria and viruses, everything from cryptosporidium to E. coli may be present in contaminated water.
The first threat, solid matter, is the easiest to deal with. Some will simply settle out if the water is left still for a period of time. A good filter will remove most solid matter and often the dirt or other suspended matter is unpalatable but not dangerous.
The second threat, chemicals, is a serious concern. Any attempt to clean contaminated water must include filter material capable of a absorbing chemical contaminants. Activated charcoal is the most common means of dealing with chemicals.
The third threat, pathogens, are also a serious issue and are most often addressed using chemical purification or boiling, though UV sterilizers are also becoming more common.
The most common way to prepare for dealing with water purification is to have a filter on hand. Whether it’s a big home-installed system like a Berkey or a small backpacker model like an MSR, these provide filtration and purification on demand. However, it’s worthwhile to spend a little time learning how to build a filter from scratch to meet emergency or on-going needs.
One common and easy-to-build design is to fill a container with layers of sand (to provide filtration of solid matter) and charcoal (to absorb chemical contaminants). Often layers of pebbles or cloth are used to stabilize the other layers so you don’t end up with channels that allow water to flow through without going through all layers. These materials can be layered into any container that you can pour water through. A bucket with an outlet on the bottom is ideal and allows you to pour water in the open top and collect filtered water flowing out the bottom. You can even build a water filter like this from a water bottle. Instructables has a nice page detailing one method. Practical Primitive has another.
It’s important to note that the charcoal used in this type of filter is not the same as the compressed charcoal briquettes you buy for cooking on a charcoal grill. Briquettes are made by compressing charcoal, but you have no idea what original source material was used to create the charcoal. If you’re using it for fuel, the requirements are much less stringent than if you’re using it to filter water. You can buy bulk bags of activated charcoal to keep on hand. It’s used in many types of filtration systems, and places like aquarium supply houses provide it in bulk at a reasonable price. Alternatively, you can make your own charcoal buy burning wood and smothering the fire before it completely burns. This technique allows you to create the charcoal you need from a known-clean source of wood. Always use wood you can trust, not things like building materials that might contain treatment chemicals.
The last threat, pathogens, can be addressed by adding chemicals like bleach or boiling. A DIY filter doesn’t help with this step, but if you can build a filter that removes debris and chemicals, removing the pathogens is straightforward. In addition to boiling or using a product like Aquapure, you might even use your backup filter, something like the MSR, which will remove many pathogens. Using the homemade sand-charcoal filter first will help lengthen the lifespan of your filter cartridges.