Reusable water bottles come in all shapes and sizes, designed to match certain aesthetics or use cases. Maybe it is meant to look nice in a modern office environment. Or maybe it is meant to pack well for a long camping trip. Or maybe it is meant to be squeezed for teammates to share during a sporting event.
Sketch cross-sections on different planes, Loft and use Shell to make the object hollow. You may need:
Right click on a part from the left menu and select "edit appearance"