I don't think any pathogen could build an immunity to silver, that would be like saying pathogens build an immunity to bleach.
The electro-chemical process that silver uses couldn't cause an immunity in bacteria since silver is not a biological agent. Much similar to other herbs that help the immune system, they are chemical and not biological in how they operate.
And even though ionic silver maybe 10ppm, there are still billions upon billions of nano particles in 10ppm ionic silver.
Though I don't discount silver mineral water, I've used both and ionic silver at 10ppm is as effective against pathogens, if not more so than 3000ppm silver minerals. But for cancer it could be a good option since silver minerals would penetrate deeper into cancer cells. Though I also think ionic silver's instability also adds to its effectiveness, which is why it takes several thousand times more silver minerals to do the same job as ionic silver hydrosol.
And when making it at home, it sure is easier to cook it with 30 volts dc with the silver electrodes sitting in distiller water, than a 10,000 to 100,000 volt ac silver electrode arc in distilled water.
Colloidal iridium and ruthenium would be good if you can afford it. Those too are made with very high voltage ac current.