More questions on silver in water filters: Is it really safe?

Dear Chen Ko

 

Thank you for your reply and I just saw your timely blog post - thank you so much! And it is so comprehensive and helpful, as always.

 

I must say the facts on silver were not terribly assuring. I have a few quick follow up questions if you could help:

 

1. I saw the info below from http://www.arkwater.com/FAQ.html. They mentioned that the silver content is 0.07%, but I don't know how that number sits with the 0.1ppm (parts per million) you mentioned. Pls advise?

Why do the ceramic elements contain silver?  Are they safe?

In a multilayer candle, the protective effect is even more critical because carbon is a natural growth medium for bacteria.  In carbon-only filter elements, which are commonly found, the carbon filter often ends up as being a bacteria repositary if not changed regularly.
The silver in the Doulton® ceramic elements is a specially formulated self-sterilizing (bacteriostatic) agent.  The result is that bacterial growth is prevented from occurring within the Sterasyl® ceramic element (which is possible with the other ceramic filter elements).  More importantly, bacterial "grow-through" is eliminated.  The silver content is about 0.07%, which is well within the allowable levels recommended by the World Health Organization and the EPA.  Because of the silver, Sterasyl® filter elements do not require sterilization after cleaning.  Oligodynamic silver in Sterasyl® is permanently locked into the pore structure of the ceramic.

2. Puzzled - why would the amount of leaching from silver in a filter increase over time? And how would changing the filter regularly help, since the silver in the new filter will also leach? 

3. I stumbled on the "perfect" solution for this silver issue. Doulton has an EWC pre-filter cartridge which is supposedly based on USA KDF system. I did a quick read on KDF and one highlight is that it inhibits bacterial growth without silver...! Having said that, I realised it is a pre-filter, meaning to say it will still go through the main ceramic filter with the silver. 😕 It sounded promising for awhile though. Any thoughts on this KDF business? Only downside is, I doubt it removes fluoride. http://www.thewaterexchange.net/what_s_kdf.html

 

4. Using the Doulton filter (Sterasyl ceramic) as an example, how much water approximately would one need to drink to consume e.g. 10g of soluble silver (or maybe not even drink, if say you wash your hands with it)? 

5. Does silver pass out of the human body...? I'm sensing that it doesn't. 😐

Dear Paloma,

1. The value of 0.1ppm as given in the previous post refers to concentration of dissolved silver in drinking water. I suspect the 0.07% quoted in the Arkwater webpage refers to the amount of silver in the filter element i.e. if the filter element weighs 100g, silver will take up 0.07g. Therefore, we are not comparing apples to apples and it becomes meaningless to compare 0.1ppm to 0.07%.
   
2. Actually, I made the statement based on my experience in many applications, including outside the topic of water. Any material will wear and tear over time, both mechanically and chemically, the latter possibly due to attack by other chemicals e.g. chlorine which is a pretty aggressive compound.
   
   As the bonds within the material break down, anything held within e.g. silver will be released. As a material ages, more bonds will be broken, releasing more stuff.
   
   Yes, you are right, a new filter will leach silver but an old filter will leach even more.
   
3. KDF (also known as redox) filters are designed to remove lead, chlorine, hydrogen sulphide and guess what, fluoride too. When combined with other filters e.g. activated carbon, they seem quite effective at removing a good variety of pollutants. I personally have not done any experiments on them but they look promising.
   
4. Assuming the 0.07% does not apply here, if you base on a concentration of 0.1ppm silver in your drinking water, you have to drink for 70 years (2 litres per day) exclusively from that silver impregnated filter before you drop from argyria or silver poisoning.
   
5. The WHO guidelines on drinking water listed silver retention in humans and animals to be 0-10% which is pretty low.

All the best in choosing your filter!