I am not sure if this should be posted here, but I'll give it a shot...does anyone have any recommendation for a water filtration system for emergency situations. Kind of like a Big Berkey, Katadyn Gravidyn or an Aquarain gravity-type units. The only issue I have read is that those units are not NSF certified. I have zero knowledge about this stuff. The Katadyn Gravidyn advertises an abililty to filter some chemicals, germs, radiation, etc...all of the info is making my head spin!! ANy help would be greatly appreciated! Thank you all.