Abstract: This invention relates to a water soluble agent including a water soluble glass containing monovalent silver ions in its glass component. In water or an aqueous solution, the water soluble glass of the invention is capable of releasing the monovalent silver ions as required in an effective amount over a long period, the monovalent silver ions excelling, for example, in eliminating or preventing the occurrence of aquatic bacteria or other aquatic life forms, sterilizing them, preventing the occurrence of algae, and preventing water contamination.