And don't forget the simple, low-tech Slow Sand Filter, suitable for many homestead and survival situations: http://www.nesc.wvu.edu/ndwc/pdf/OT/TB/TB14_slowsand.pdf

If you're not looking for the most expensive, highest-tech, most-chemicals-required way to filter water, go with a method that is well over 100 years old, and is still used in some municipal facilities.

Some slow sand filters would look awfully good in many places in Japan right now...

Sue

Thank you for saying about the alum method - that's a really good way to start before the purification process and it's dirt cheap if you just pack some with you. It will bind to many of the nasty gunk in water, drag it down and you can separate it. Then from there do your normal distillation/boiling + filtering and that will give you about as good as you're going to get unless you have a reverse osmosis system to use in addition/aside from that.

Excellent article on it:
http://www.wikihow.com/Purify-Water

And that ladies and gents, is (IMHO) the best process we have available.

Susan ... thanks for posting the slow sand filter. Very practical. It won't remove everything, but could be very useful in a disaster situation. And it's pretty easy to construct. Maybe it would work even better if people mixed some charcoal with the sand - the charcoal might absorb some chemicals. Don't know if this would be an improvement. Just thinking out loud. Anyway, thanks for the link!

For water in urban sources, my own approach in L.A. will be to scavenge clean water from various locations such as water tanks, pipes, storage containers etc. I plan to work harder on developing this set of skills this year. I realized that I need a few items/tools
some garden hose
some sort of hand-powered pump
something that can drill a hole (or punch) through sheet metal

Pete #2

It is a nice rainy morning here in SoCal, a timely reminder that collection of rainwater/dew can be a viable source of good water, although that would not be the case in northern Japan right now....

For a charcoal filter, will any charcoal do? Is there a particular method to prepare it if you have to make your own? Charcoal is used in military chemical protective filters and suits, so I imagine it does work. How does it work, scientifically?

Montanero - I can help with part of the answer. No doubt the best thing to use for absorbing chemicals in water is proper charcoal (activated charcoal) available in stores. This charcoal is probably higher purity.

However, in primitive villages in the third world I know people who use charcoal (from campfires) for the same purpose. It is routinely used when they wash out gourds - which are used for storing liquids. Gourds can be used for water storage, but they are also used for storing milk and the preparation of "sour milk" (i.e. milk aged for 12 hours and deliberately soured before drinking). When the gourds are cleaned after the milk preparation, the people wash them out with a mixture of water and charcoal (from the firepit) to absorb impurities. Subsequently, any water from the gourd can taste a bit "ashy", but is essentially harmless for drinking. So my guess is that you could use charcoal from a campfire as a crude method for absorbing impurities in water.

Pete #2

Susan ... I was thinking a bit more about the sand filter. A couple of things came to mind. The first is that you would need to have clean sand. If the sand has any salt or soluble minerals, they will get into the water. This is probably why the folks in Japan are not using this method in the tsunami zones. All the local dirt and sand has been contaminated with seawater.

The second thing is that some of your water will stay in the sand - the sand will remain wet. So you will lose some water when you use this technique. If you have a major source of water, then this may not matter at all. But if you have a very limited water supply, then you may not want to lose some to the filter. In that case, it may make more sense to filter impurities (dirt, algae) with some layers of cloth.

Pete #2

Montanero ... a bit more information on charcoal. It seems that the 2 advantages of charcoal is that it has a tremendously high porosity and it does quite a good job of absorbing organic chemicals. The high porosity means that it has a high "active surface area" - which simply means that even a small amount of charcoal has a lot of internal sites where chemicals can attach to the surface. Although basic charcoal will work, companies often take it and subject it to further processing. This produces "activated charcoal" which has even higher porosity, and it also has a special surface treatment that increases the ability of chemicals to bind to the surface.

Besides water filtration, charcoal is used medically (medicinal charcoal) to absorb poisons from the stomach and intestines. Doctors give it to patients for that reason.

I have been looking to see if i can find any information about charcoal produced by burning different kinds of woods. I have been wondering about whether the charcoal from a certain type of wood might be superior. I am just curious about how best to produce useful charcoal from a campfire. But I haven't found any good sources of info yet.

cheers,
Pete #2

Here is some basic information on activated charcoal:

Activated Charcoal

Pete

I produce a fair amount of agricultural charcoal (biochar) to improve the soil in my garden. It's incredibly simple to make. You burn wood through the "gas" phase and then deny oxygen so it can't burn in the "carbon" phase.

In practical terms: make a fire in a safe pit, keep adding wood, and continually tamp down the pieces that have stopped burning vigorously and have turned to carbon. Than, dampen it slightly, cover to exclude all oxygen, and let it sit until cold.

You can also heat wood that's stuffed inside a closed (not sealed) vessel. You'll get less ash this way. An uncoated tin can with a foil cover is an easy way to experiment.

Activation of the charcoal is a separate process, and I'm not sure a backyard setup could do this effectively. Though since my charcoal finishes while exposed to some steam and some CO in a sealed environment, I wouldn't be surprised if it is activated to some degree (can't prove it though).