Colloidal silver is a mixture of solid particles and a liquid... particles are small and support a charge; the zeta potential; generally they can stay suspended as a colloid indefinitely.
Ionic Silver is a silver compound. The silver is usually disassociated in distilled water to form the Ag+ or Ag2+ cation, and an anion, the anion generally a hydroxide or oxide [Ag2O]... most often a neutral silver carbonate is formed as well as a hydroxide attracts CO2 from the atmosphere...
This is what natural water bodies contain to one extent or another, generally as a calcium or magnesium, not silver... and why the oceans and bodies of water are absorbing CO2 from the atmosphere.
In other words... it is not the silver that makes it effective.
When water is evaporated from ionic silver, the remaining solids are compounds silver carbonate, and silver hydroxide; which depends on what anions where in the ionic solution with the silver.
Same thing that happens to the calcium in lime water upon evaporation of the H2O.
And why, throughout history going back at least to the middle ages (as far as I have taken my research), people in the *know* (Medieval monks, physicians, etc.) washed their hands in a weak sollution of lime water to help prevent the spread of disease.
So yes, such a silver solution works... so do other such solutions of calcium or magnesium.