Yes, you may add electrolytes, drink mixes and other flavorings into your GeoPress when it is equipped with a New! GeoPress Cartridge (V2) and a One-Way Electrolyte & Drink-Mix Valve. For bottles equipped with a cartridge sold pre-April 2023, we do not recommend adding flavoring or electrolytes directly into your GeoPress because it can decrease the lifespan and efficacy of your cartridge. Instead, we recommend you pour your clean drinking water from your Grayl into another water vessel containing electrolytes or flavorings. Alternatively, upgrade to a GeoPress Cartridge (V2) and add a One-Way Valve.