Just wanted to comment: it absolutely should be pure distilled water, and hotter is better (if faster is better). Using tap water will result in a nasty funk being generated as all the impurities in the water react to the silver and the electricity. Now, there is a kind of funk which appears on the silver wires themselves; that can be wiped off and most of it (maybe not all) will come out still attached to the wires. (Unbleached coffee filters will take the rest of it out.) The kind of funk that comes from using impure water will turn the whole batch into a nasty dark grey color (or, at least, the water in my area does). So please, don't think of distilled water as a "nice to have". It's vital to use only steam distilled water when making Colloidal Silver .