PW
Carbon filters do remove microbes...
Here is an excerpt and a link to the entire article. What carbon filtration doesn't do can be seen in the remaining three categories of the EPA contaminant list. Carbon is mentioned as a treatment for only one of the four Microbiological contaminants listed: turbidity. It is not recommended for coliform removal or for cysts, though ironically, some of the very tight solid carbon block filters now on the market remove bacteria (though manufacturers seldom make this claim) and cysts like giardia and cryptosporidium quite handily. Multipure solid carbon blocks, in fact, were the first filtration device certified by NSF (the most prestigious independent agency that tests and certifies product performance) for removal of cryptosporidium. Multipure and some other very tight carbon block filters remove cysts simply because of their restricted pore size. Multipure blocks are absolute 1/2 micron filters, making cryptosporidium organisms about ten times too fat to go through the holes. Thus, although other types of very tight filtration might work as well, the very dense carbon block filters now on the market are very effective against certain forms of microbiological contaminants.
http://www.purewaterproducts.com/articles/carbonIt was not my intent to go quite so far afield, again in a pinch anyone can make a charcoal filter that will improve the quality of unidentified ground water. As OP pointed out even a sock full of sand will have some benefit.
And like Bearhunter, I have consumed a lot of ground water and never suffered a moment of discomfort. And before we get into the "Chicken Little" the sky is falling, just remember, you will die of dehydration before the "microbes" can get you, so rather than die of thirst, if it looks like water drink it...!