19 Water Purification: Chemical Treatment: Silver:
Description
This article is from the Water Treatment FAQ, by Patton Turner with numerous contributions by others.
19 Water Purification: Chemical Treatment: Silver:
Silver has been suggested by some for water treatment and may still be
available outside the US. Is use is currently out of favor due to the
EPA's establishment of a 50 ppb MCL (Maximum Contaminate Level) limit
on silver in drinking water. This limit is set to avoid argyrosis, a
cosmetic blue/gray staining of the skin, eyes, and mucous membranes.
As the disease requires a net accumulation of 1 g of silver in the
body, one expert calculated that you could drink water treated at 50
ppb for 27 years before accumulation 1 g. Silver has only be proven
to be effective against bacteria and protozoan cysts, though it is
quite likely also effective against viruses.
Silver can be used in the form of a silver salt, commonly silver
nitrate, a colloidal suspension, or a bed of metallic silver.
Electrolysis can also be used to add metallic silver to a solution
Some evidence has suggested that silver deposited on carbon block
filters can kill pathogens without adding as much silver to the water.
Katadyne markets a silver based water treatment product called
Micropur. The manufacturer recommends a 2 hr contact time at a dose
of 1 tab per liter and states the product is "For the Disinfection and
storage of clear water. Reliably kill bacterial agents of enteric
diseases, but not worm eggs, ameba, viruses. Neutral to
taste...insure protection against reinfection for 1-6 months." The
following forms are available:
Micropur Tablets MT1 1 tablets/qt 25 gal
MT2 1 tablet/5qts 62.5 gal
Micropur Fluid MF 75 10 drops/gal 75 gals
MF250 " "250 gals
Micropur Crystal MC250 1 packet/gal 250 gal
MC 2500 1 spoon/25 gal 2500gal
MC12500 1 spoon/250 gal 12500 gal
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