First, keep in mind that if you suspect the water has ANY chemical contamination then it must be discarded immediately. This includes surface run-off from a farm, oil, sewage.....
Second, it must be a 'freshwater' source, not sea water. (I'll come to that later).
You are looking to perform two actions to make water potable. The first is filtration, the second is purification. Filtration is to remove anything that makes the water not look like pure water (in simple terms). Suspensions, sediments, floaters, anything that makes it cloudy....anything that isn't actually 'dissolved'.
To make a simple yet effective filter, construct the following:
- Find a 2lt coke bottle (with lid!), pierce a hole in the lid and screw on.
- Cut the base of the bottle away. (keep the bit you've chopped off and use it as a collection device!)
- place a screwed up piece of tight woven cotton (denim works) tight in to the lid of the upturned bottle. Keep the bottle upturned now.
- Fill about 2 inches with wood ash.
- Fill about 2 inches with small charcoal.
- Fill about 2 inches with larger charcoal.
- Fill about 2 inches with sand.
- Fill about 1 inch with pebbles.
- Fill the rest with Sphagnam Moss / clean cotton clothing.
With the ingredients here, you will remove anything right down in to the larger micron-size particles. Pass your water through a number of times until you see clear water come through.
This is NOT yet ready. You may still have bacteria/viruses present in the water.
Next, (if you have them), add a PuriTab, according to its specific instructions.
Finally, the ol' "rolling boil" for 5-10 minutes. Be careful not to actually boil too much - you don't want your water evaporating away.
The puritab option is an optional extra there but one I would definitely advocate.
So, seawater. There are two options here and both entail evaporation and distillation.
The simplest method that I have found for this is a decent solar-still.
- Dig a shallow hole in the ground (somewhere in direct sunlight)
- Place a container with your seawater (or other water source) at the bottom of the hole.
- Place an empty container inside the first container - being sure that the water does not spill in to your new container.
- Cover your hole with a sheet of clear plastic and weigh it down around the edges.
- Place a pebble in the middle of the sheet, directly over the second (empty) container.
- Leave for a while.
When you come back, you 'should' find that the water from the first container has evaporated, condensed on the underside of the plastic sheet and has run off in to the second container. You risk any water collected in your pot evaporating away too. It's not particularly efficient but it used the least resources.
A second method requires a metal container with a lid,a 2 foot piece of hose and a collection container.
- Pierce the lid of the container and instert one end of the hose.
- Fill any gaps around the hose-entrance with glue, pine resin (mixed with ash) or wax.
- Fill container with lid and replace lid (with hose now attached).
- Boil water over a fire.
- Steam from the water will travel along the hose, cooling as it does so and collecting as water at the far end in to the collection container.
If steam comes out of the hose instead of water, look for a method of cooling the hose, such as covering it in a layer of cold soil/mud.
So why do we not use chemically contaminated water? The problem is that firstly, you cannot filter out chemicals. Secondly, the boiling won't kill the chemicals (it may actually exacerbate their effects!). Finally, many chemicals have boiling points much lower than water - the solar still will cause the chemicals to evaporate and condense in to your container before the water.
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