Except instead of foil you have really really tiny silver particles, and the suspension medium is distilled water.

Why make colloidal silver? Some claim it has anti-bacterial, anti-fungal, and anti-viral properties. It can be applied topically (i.e. a burn or cut), ingested, or added to water to help purify.

http://en.wikipedia.org/wiki/Medical_uses_of_silver

Here's my setup:

Here's What You See
* Two gallon water container: I cut rectangular holes in either side near the top where I can slide in my silver bars, and drilled a hole in the plastic top where the air hose can run
* PPM (parts per million) meter: I got this from Amazon. Low cost (like 20 FRNs) and pretty cool.
* Small laser pointer: You'll see why I have this later in the write up.
* A variable voltage, 1300mA DC power supply: This provides variable voltage across the silver bars. 12v, 9v, 7.5v, 3v
* A small fishtank air pump & tubing: I run the air tubing through a small valve (so I can throttle down the air to just a trickle) and then through an in-line filter before it enters the water container