Ask the Expert: Ceramic Filters

Q: I am curious about the cleaning of MSR ceramic filters. All instruction manuals indicate that the ceramic filter can be scrubbed and rinsed to expose a newly useable layer of ceramic, and they do indicate that clean water should be used in the rinsing. I haven’t found any reference to the importance of using clean water. I am trying to convince a group of backpackers that their technique of washing the filter off in the stream they are filtering water from is contaminating the clean water supply, but cannot find any sources to validate my claims. Do you know of any research, articles, or references I could point them towards so that I may hike safely with them in the future?
Colleen Lambo
Cincinnati Zoo and Botanical Gardens

A: I don’t know of any legitimate peer-reviewed research data out there to conclusively validate or invalidate the question. Anecdotally from my experience with Katadyn and Doulton/Fairey Industrial ceramic products in military and civilian applications, the manufacturers emphasize ‘clean’ water for the scrub and rinse to ensure that the cleaning process doesn’t introduce additional large particles/biofilm that would subsequently plug the pores in the ceramic candle and negate the benefits of the scrubbing.

I hope that comfort can be given towards contaminating the clean water supply by thinking about the net organic/pathogenic loading from the small quantity of contaminant being scrubbed off into the stream and realizing it is really no worse than the excrement from a small mammal or bird (fish also excrete in streams). The small volume is quickly diluted and oxidized, so I certainly wouldn’t lose any sleep over it. The miniscule amount of ceramic that is scrubbed off is diatomaceous and no different than the bulk of insoluble sediment in the stream already. If one wanted to be extremely careful, the bulk of the material could be scraped off into a cat-hole (located at least six feet from the water source), rinsed into the hole with water taken from the stream and then burying it all.
Greg Reyneke, CWS-VI
Red Fox Advisors

A: I concur with Greg’s assessment of the cleaning process of the ceramic surface of the filters. If the cartridges are open on both ends, then it would be a fatal mistake to rinse those in an open stream or other non-potable water source. The candle-type filters that are closed on one end are recommended for the outfitter program. The outlet tip of the filter can be capped to keep the internal area of the filter from being contaminated. I would recommend keeping a separate cleaning vessel dedicated with a known water quality for cleaning. This will take a little bit of planning but it is well worth the effort when you consider the health problems associated with Giardia lamblia and other pathogens that can create gastrointestinal problems that require harsh antibiotics to restore health.

When cleaning the filter(s), use a good plastic stiff bristle brush for scrubbing the outside of the ceramic cartridge. Another point that should be taken into consideration is the care of your hands. If you have open cuts or abrasions on your hands, you would be well advised to pack several pairs of latex gloves to help prevent getting any bugs from setting up housekeeping internally. It is always advisable to wash your hands thoroughly after cleaning the cartridge so you don’t accidentally ingest the very thing you are trying not to ingest in the first place.

As an aside, there are some very high-quality drinking water straws that claim 99.999-percent removal of pathogens from the water that are easy to pack and maintain in the field. These straws use a special porous membrane that has proven to be as effective as the ceramic filters. Perhaps the writer could research that as well. I will look into this issue further at her request.
Gary Battenberg
Good Water Company

A: I think the whole purpose in cleaning these filters is to remove whatever is clogging them up without getting any of it on the inside of the filter. To that end, I don’t see any reason to use a clean water source or not to use a questionable water source. Whatever is available.
C. F. ‘Chubb’ Michaud, CWS-VI
Systematix, Inc.

Editor’s note: Some discussion resulted over the possible use of urine, as it has been widely believed to be sterile. A recent study from Loyola University, however, disputes this position. It indicates urine is not sterile and does indeed harbor bacteria. In response to the additional information, the following comments were elicited:

“It would certainly be better to use clean water, but I would not use urine. The good side of rinsing off the residue in the stream is that it won’t have the concentrated contaminants that are on the surface of the filter.”
Peter S. Cartwright, PE
Cartwright Consulting

“The key is clarity or lack of solids in the cleaning fluid. The word clean shouldn’t be inferred to mean sterile, merely ‘clear’ – devoid of large particulates and suspended solids. The cleaning fluid is used on the influent side of the ceramic barrier, so any pathogenic/non-pathogenic organisms will be captured and prevented from passing through to the other side, assuming that they’re larger than the filter’s absolute pore size. A smart hiker will understand the dynamics of the tools that they are using for life preservation and work with them accordingly. From a practical perspective, microfilters like this are designed to reject sub-micron particles, and a properly designed/deployed prefilter is key to minimizing maintenance. The challenge presented to the filter should be proportional to the pore size. Pumping muddy sludge into the filter will plug it much faster than allowing turbid water to settle, or even filtering it through a simple filter to clarify. An old sock is better than nothing as a prefilter to prevent large particulate from plugging the ceramic.” Greg Reyneke

“I see no need to be concerned with drying. Just don’t get questionable water used for cleaning on the INSIDE of the filter. These filters works as barriers. Water can squeeze through the pores but critters cannot.” C. F. ‘Chubb’ Michaud