I have been trying to find an emergency, gravity fed water filter that will provide at least 1 gallon an hour of clean drinking water from any non salty source (river, stream, pond, lake, mud puddle, swimming pool, etc) that costs less than $100 dollars. The Berkey, British Berkefeld, Katadyn Drip, Durand and a number of others all fit the bill except that they cost $200 and up. I could fire my own ceramic filter, impregnate it with silver and include some charcoal but after all that I would probably be over $100. The filter I have found that fits the bill is the Just Water Ceramic Filter manufactured by Winfield and Black Jack Industries and sold by the Monolithic Marketplace. The product is a dome shaped ceramic filter you insert into a hole in the bottom of a bucket and let it drip filtered water into a container below. You can buy just the filter ($23.50) or if you are short on buckets a set of buckets and the filter ($43.45). I do not have one yet but I just put in an order. Here is the site with specifications: Monolithic Marketplace Water Filter Of course with all ceramic filters the less turbid the water you use the better so I am going to use mine for rain water off of my roof. But if I were short on clear but unpurified water I would build a sand filter in another bucket (drill hole in bottom of bucket, insert screen, fill bucket half full with sand) to filter the dirty water into the bucket where I have the ceramic filter and then into the bottom container of fresh purified drinking water. Carl.