Question:
I've been researching methods of water filtration by slow sand filtersin hopes of thinking of ideas for an 11th grade science exeriment. Ireally don't know where to start, though I understand the basicprinciple of filters. I can't really test the presence and types ofbacteria because I'm not a scientist in a lab but I can deal withsimple sand filters. Anyone have any expriment/test ideas that have todo with water filtration or improving upon slow sand filters?

Answer: Good place to start:http://en.wikipedia.org/wiki/Slow_sand_filter_bed

And don't try to reuse sand.

Bacteria and viruses are really tiny. They'll pass through most filtersdesigned for hikers and campers. Those filters are meant to removeGiardia cysts which are much larger. The way those filters are supposedto be used is to start with fairly clear, unpolluted water, filter, thensome method of "water purification" to kill or remove all water borneorganisms.

"Purify" has a somewhat different meaning with drinking water.

My favorate chemical water purification is the iodine based Polar Pure:

http://www.polarequipment.com

Chlorine (in a concentration you'd want to drink) won't kill all typesof organisms. Chlorine works for city water because they use a known,reliable water source and back it up with testing.

Charcoal is used in some filters to absorb certain dissolved chemicalsin the water, but it won't absorb alcohol or petroleum type chemicals.Charcoal is made by heating wood in an oxygen starved environment.Activated charcoal is charcoal made porus so it is substantially moreabsorbant.