The preparation of nanocontainers with a hydrophilic core from water-in-oil emulsions and their subsequent transfer to aqueous medium is crucial because it enables the efficient encapsulation of hydrophilic payloads in large quantities. However, major challenges are associated with their synthesis including low colloidal stability, leakage of encapsulated payloads due to osmotic pressure, and a demanding transfer of the nanocontainers from apolar to aqueous media. We present here a general approach for the synthesis of polymer nanocontainers that are colloidally stable, not sensitive to osmotic pressure, and responsive to environmental stimuli that trigger release of the nanocontainer contents. Additionally, the nanocontainers can selectively deliver one or two different payloads upon oxidation and changes of pH or temperature. Our approach uniquely enables the synthesis of nanocontainers for applications in which aqueous environments are desired or inevitable.