sounds good?

Here is how the Big Berkey Water Filter Systems Work
Without getting too complex, several methodologies are utilized by the Black Berkey purification elements. The elements are composed of a formulation of more than a half dozen different media types constructed into a very fine matrix creating millions of micro-fine pores. The pores are so small that pathogenic bacteria, cysts, parasites, sediment and sedimentary minerals are not able to pass through them. The media formulation both “absorbs” some contaminates and “adsorbs” other contaminates. Next, heavy metals ions (mineral molecules) are extracted through an Ion exchange process where they are essentially electrically bonded to the media. Finally, our filter elements are designed such that each water molecule can take several minutes to pass through the filter elements whereas these molecules passing through other filtration systems pass through those filters in literally microseconds. The longer the water molecules are in contact with any media, the greater the removal of the various contaminates. – BigBerkeyWaterFilters.com

These are the features and benefits of Big Berkey Water Filter Systems as stated on their website:
Highly polished 304 stainless steel shell
Will filter bacteria to a 99.99999% leve land viruses to a 99.9999% level.
The black berkeys filter out Chlorine to undetectable levels
Removes Lead, MTBE’s, and other heavy metals up to 95% levels.
PF-2 filters remove Fluoride and arsenic.
Black berkey filters exceed EPA log 7 ANSI / NSF protocols for filtration and are rated as water purifiers.
Gravity fed systems that require no plumbing or water hookups for use
Black berkey filters have 3,000 gallon life (6,000 used in pairs)
Allows red dye testing to know when filters need replacing (no expensive water tests)
In emergencies allows use of non-public water (stream, lake, etc.) Tweet