Table 4.

Concept changes after expert evaluation.

App feature/characteristic	Prototype I	Prototype II
Challenges	Strict defined rules to reach goals	Easing the rules: More jokers for the users of the drinking world in the Big Master level
Feedback	Visual feedback	More visual feedback, for example, a smiling avatar for rewarding consumption of water
Feedback	Informative feedback (tips)	Optional extra button for more information, the user can choose if he/she wants more information concerning feedback
Feedback	—a	Reflective questions in feedback, for example, What are your best tips for a friend to encourage him to drink more water?
Feedback	—	Goal-orientated feedback: Asking an introductory question, linking the tips to the answer and thereby to the user’s goal
Usage motivation of app	Feedback development: Focus on preintender and intender	Informative feedback focuses on intenders only, preintenders are not considered. This decision was supported by literature, as health apps are more likely used by health-conscious people [31]
Worlds	—	Bonus worlds: Might be possible with an update of the app (menu button bonus worlds)
Worlds	Worlds are started one after the other	The worlds can be played simultaneously
Infothek	Point-related access or as a present	More frequently access: Through reduction of the distance of the points
Infothek	Information about healthy snacks/drinks	Including more information about healthy snacks and drinks
Infothek	Health, food waste, and beauty are topics	Content ideas for the following topics: (1) Health : Where does enjoyment of taste start and where does it end (start of addiction); mechanism of resorption of nutrients; food waste: Shelf life of food, seasonality of fruits and vegetables, environmental pollution; (2) Beauty: Cosmetics without any animal testing
Quiz	Answering question with yes/no; assigning answers	Answering questions with drag and drop mechanisms

^aNot applicable.