A sealed indicator vial to detect the presence of a predetermined contaminant in water containing a mixture of reagents reactive in the presence of water, the mixture being sufficiently dehydrated to prevent the reaction of said reagents while sealed in said vial. The vial contains an inert atmosphere at less than atmospheric pressure. Also described is the method of producing such an indicator vial in which a tube containing the dehydrated reagents is heated and stretched to form a narrow waist while under vacuum.
