[A] = Purification Standards: Element must remove/inactivate all types of pathogenic organisms. Specifically, element must remove two species of virus to 4 Log10 (=> 99.99%) and remove pathogenic bacteria to 6 Log10 (=> 99.9999%) and remove cysts to 3 Log10 (=> 99.9%). This makes Berkey systems the only true gravity fed purification systems.

Purification Challenge: The Standard has selected 3 types of challenge organisms: Bacteria (Klebsiella terrigena), Viruses (Polio and Rota) and Protozoan Cysts (Giardia or Cryptosporidium).

• 1.  VIROLOGY - Demonstration of a 4 Log10 (99.99%) reduction is required on the combined polio/rota virus challenge matrix.
• 2.  BACTERIOLOGY - Demonstration of a 6 Log10 (99.9999%) reduction is required for the Klebsiella terrigena bacterial challenge.
• 3.  CYST REMOVAL - Demonstration of a 3 Log10 (99.9%) reduction is required for the cysts using Cryptosporidium or Giardia.

[C] = Aqua Crock, Doulton GSS-2, Ceragrav LP-5 all use Doulton Filter Elements - life expectancy is 525 gallons or 6 months, whichever occurs first.

[D] = Claim made is 2 years or 3,000 gallons; while the manufacturer of their Doulton filter elements states the life expectancy is 535 gallons or 6 months whichever occurs first.

[E] = While the company claims their elements will last for 3,000 gallons on their comparison chart, we used the claims of the manufacturer, which state that the life of the elements is only 1,500 gallons or 12 months whichever occurs first.

[F] = Calculation based on each element producing 3 gallons when used for 12 hours per day during 365 day maximum recommended time limitation.

[G] = Calculation based on each element producing 12 gallons if used for 12 hours per day during 182 day maximum recommended time limitation.

[H] = Cost per gallon presumes maximum gallon claims reached prior to "replacement time limitation" above and calculated based on "max daily output" above, whichever is less or occurs first.

[I] = Successfully demonstrates removal of microscopic red food coloring particulate from source water at 1 tablespoon of red food coloring per gallon.

[J] = Test is designed to determine if high turbidity (larger particulate) source water will clog up elements which may render them ineffective during actual emergency conditions. 1 tbsp carbon dust per gallon. Flow rate reduction of <25%=Pass, >25%=Fail.

[K] = NSF Claims: No listing on NSF website as of publication date. NSF has confirmed that ProPure has not been certified by their organization

Where information was available and published, this information was used. Where information was not available, information was calculated, such as in F and L above, using the available published information. Where published information on systems was in conflict with the published information by the manufacturer, such as in C, D, and E above, items are highlighted in orange.

Data based on manufacturer's life expectancy claims rather than the claims of the manufacturer's customer. Information collected from websites, corporate literature, internal testing and outside independent sources is believed to be accurate at time of publication (5-15-12). Neither this chart nor it's producer assume any liability, implied, expressed or assumed.

There are other gravity fed filter systems that claim they are not to be used with microbiologically unsafe or questionable water. We chose not to include those systems in this comparison chart.