Australian scientists have discovered that by coating regular sand as found virtually anywhere with "functionalised" graphite oxide, it produces a highly efficient filter vastly outperforming regular sand and being far cheaper than activated charcoal. The process can apparently be done at room temperature, and from the following articles looks quite impressive. http://www.physorg.com/news/2011-06-super-sand-purification.html http://nextbigfuture.com/2011/06/super-sand-for-better-purification-of.html http://www.bbc.co.uk/news/business-13895077 It is believed this will be a great benefit to anybody faced with drinking dirty water. For people in Africa especially, this could be an affordable life-saving product as the graphite used can be produced as a waste material. I've not looked into the process, but I don't think it's particularly complicated or fussy. I've not seen if it can remove biological contaminants, but I see no reason why it should not do so. If proven successful as it seems, I think it likely we see it become a major source of ad hoc water purification. Also, If you use activated charcoal to purify water, it works better if mixed with the sand rather than packed in layers according to an article on BBC radio.