Regarding some of the ...

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Regarding some of the responses to my earlier comment on the limitations of silver:  Chlorine and other primary disinfectants are broad spectrum, and effective in seconds to minutes. Studies that test silver against coliform indicator bacteria are not reflective of performance against many pathogens. Silver is slow acting and has a limited performance data base against non coliforms. Many of the published studies used laboratory  deionized water as the medium, which negates the results. The internationally reviewed WHO report is extensive and up to date to its publication date.  Drinking water doses cannot be higher than about 50 to 100 ppb because of the argyria possibility. Silver works selectively in plumbing to suppress legionella growth, where it has multiple hour contact opportunity. Silver impregnated activated carbon point of use systems, where silver is allowed as a potential biostat for regrowth of HPC bacteria on the  filter, but NOT as a biocide for the water,  have limited and temporary efficacy even for HPC suppression .  Ceramic or other filtration systems are beneficial, per se, but the role of silver, separate from the  filtration, is debatable. Silver also can be affected by presence of other ions like chloride in the water. And by the way, silver is known in some cases to have induced resistance in some bacteria, so it can lose whatever efficacy it had. Silver has its place, but NOT as a universal and broadly acting municipal  water  drinking water disinfectant!   To the silver  advocates: please tell us what the CT values are for silver versus a broad spectrum of bacterial, viral and protozoan pathogens.

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Still waiting for that WHO study that indicates problems with silver ceramic filters and water treatment.  Please furnish additionally the information on the particular ceramic filters since there are many differences from one to the next.

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Thanks for the expression of concerns about water filter media of granulated ceramics.  While this looks like an argument it could rather be viewed as a useful set of questions.  It would be particularly interesting to see within those studies of silver treatment (wherever it is) the details of the silver treatment and why in heavens name this is slow acting.  To look only at effectiveness against pathogens is most certainly not enough.

One should not disparage the excellant work of the WHO in their sanctioning ceramic pot filters, which incidentally have been verified in treatment of E.coli to log 10.0 effectiveness.  That for the filters tested these had not been properly treated with silver is even more interesting.

About the possibility of those drinking water the water of silver treated filters getting argyria (the cosmetic condition caused by ingesting some forms of silver), filters that are properly treated with silver are well within the EPA limits of silver leaching, at 100 micrograms per liter.

Before debating the efficacy of silver in a ceramic filter medium it is first necessary to seek out the relevant studies.   It should also be noted that claims of silver effectiveness take into account what is clearly the number one contaminant, responsible for the greatest numbers of illnesses and deaths: pathogens.  Other contaminants need to be dealt with in other ways. 

By the same token, claims for municipal-style water treatment, using granulated silver media, are intended in combining the two steps of filtration and disinfection into a single step.  These do not account for such other needs of water treatment as those of other contaminants.  Then again, for example, turbidity can be remediated by simple processes of settling the particles out, without certain products or chemicals.

It should be noted that in many developing world communities the only problems with the water are pathogens and turbidity. Treatment intended to deal with all  conceivable problems with water are quite obviously too expensive.

Once again, referencing WHO guidelines, for such water treatment as is necessary in the developing world, reduction of E. coli is regarded as the pragmatic approach; an indicator for other pathogens. To suggest the need to lab test a great many other pathogens is to make water treatment too expensive for the needs of the poorest.  We need a realistic business model!

Otherwise a big part of what needs to be discussed is arguments on two sides, by experts who are equally knowledgeable; rather a moral question. Do we insist on the highest standard for all:  log 5 or log 6 effectiveness?  Or do we allow for what will get safe drinking water to the greatest number of beneficiaries:  log 4 or even log 3 effectiveness?  Insisting upon log 5 or 6 will most certainly not achieve the 2030 goals, or even by 2040 or 2050!

And by the way, over what period of time will those municipal-style treatment, supposedly sustainable facilities in low income communities be monitored and evaluated?  Two years is not good enough. Make it ten!  In the spirit of seeking answers any thoughts are appreciated.

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