just add waterjust add water from plus minus design features a sports cap that has the ability to seal onto almost all plastic water bottles that are currently on the market through an intuitive push and twist action that mimics traditional screw fit tops. once you have fitted one of the caps to the bottle, the top section tightens to create a seal. flavor tabs are also available in a range of flavors. what a great idea - it takes so little to make a huge impact.