You can purchase hydrated jelly beadz. Or if you prefer you can purchase dry jelly beadz and hydrate them yourself. If you have purchased dry, follow the instructions on the label - add water to the beads and allow to bloom for 6-8 hours.
Fill your water bottle about half full with Orbeez.
Blow up your balloon. Twist the end of the balloon to prevent the air from escaping.
Lay the bottle on its side. Keeping the balloon twisted and the air still in the balloon stretch the end of the balloon over the top of the bottle.