Hi, AlchemySA, Welcome aboard!
In North America, water purification by colloidal silver is routinely accomplished in Mexico using a high-ppm CS manufactured by the mill method. If I am not mistaken, its manufacture is a monopoly of the Mexican government. The name of the product is 'Microdyn." You can find a good deal of discussion in the archives concerning Microdyn. I don't know if it can be imported legally to the US or other countries. Best regards, Matthew
