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I was in China recently, and the tour guide mentioned that in some parts of China, the water quality is not good (due to pollution). To get around this problem, some locals used solid silver and boiled it together with water, so that "germs in the water can be killed off".

I am no expert in chemistry, but I'm skeptical whether this even works. Wouldn't it be even more harmful to boil water together with silver?

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This World Health Orgainization report explores silver as a water disinfectant. It kills a wide variety of bacteria, and fungi without leaving a residue or many chemicals in the water.

Silver has been known to have antibacterial properties since Roman times, however, the increased use of nanosilver in a range of (as yet largely) ex perimental drinking-water treatment systems, its use in conjunction with ceramic filters and its perceived potential to be a water disinfectant that does not result in disinfection by-products (DBP) in the treated water have raised the profile of this chemical.

Silver and AgNP have been shown to have general (i.e. not specifically water disinfection related) anti-bacterial properties against a range of both Gram-negative (e.g. Acinetobacter, Escherichia , Pseudomonas, Salmonella and Vibrio) and Gram-positive bacteria (e.g. Bacillus , Clostridium , Enterococcus , Listeria , Staphylococcus and Streptococcus) – Wijnhoven et al. (2009). Some researchers have also demonstrated that fungi, such as Aspergillus niger , Candida albicans and Saccharomyces cerevisia, are sensitive to silver (reviewed by Marambio-Jon es and Hoek, 2010). In addition, a number of studies have suggested a bioc idal action of AgNP against hepatitis B virus (Lu et al., 2008), HIV-1 (Elechiguerra et al., 2005), syncital virus (Sun et al., 2008) and murine norovirus (De Gusseme et al. , 2010).

Later on (page 4), the report summarizes research on how quickly silver kills pathogens. Silver works relatively slowly, but hangs around for a while.

It can be seen from these studies that log reductions varied widely with some bacteria being more sensitive to silver (i.e. more easily killed or ina ctivated) than others. Generally, relatively long contact times were required to effectively reduce bacterial concentrations (e.g. 3 hours or longer), ...

I wasn't able to find anything specifically about how boiling combines with silver, but it seems like the two treatments should go together pretty well. Boiling works quickly and kills all of the bacteria, but once the water cools it can be reinfected if it isn't drunk soon. Silver works slowly and inhibits bacterial growth even at low concentrations. Sounds like a good one-two punch.

  • What surprised me about the claim was that it wasn't about silver nanoparticles, but about a lump of silver. My [unreliable] intuition is that boiling silver in water doesn't lead to nanoparticles, and would grossly reduce the surface area, requiring much longer for the reactions. This is just to say: This answer doesn't seem to address the difference in the treatments. – Oddthinking Sep 24 '18 at 3:56
  • @Oddthinking The effect doesn't need nanoparticles (presumably they speed it up). It works with bulk silver (and, to some extent, copper). Hence the probably reason why people like the Romans used silver vessels to store water when they could. – matt_black Sep 24 '18 at 9:40
  • @matt_black: If nanoparticles require 3 hours, how long does bulk silver take? A week? Can it even keep up with the settling of new bacteria from the air? <--- This is ill-considered speculation, and is probably wrong. What do I know? But there is a gap in the answer, because it doesn't address that. – Oddthinking Sep 24 '18 at 14:28
  • @Oddthinking I don't know. But I suspect that, since the romans found silver vessels to be useful, the issue is probably killing water-borne bugs not those that come from the air (which may be unimportant most of the time especially for covered vessels). If they noticed an effect, it probably works but might take hours. It would be good to see more sources from real studies. – matt_black Sep 24 '18 at 16:40
  • Nanoparticles are a red herring. The ions do the work, and the nano-particles are just hanging out. They may increase the surface area available for ionization, but they do not themselves kill bacteria. news.rice.edu/2012/07/11/… – BobTheAverage Sep 25 '18 at 13:46

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