- Refill them with sand or another substance and use them as workout weights
- Refill them and use them as weights for your picnic or beach blanket
- Fill them with something heavy and use as a doorstop or paper weight
- A drip irrigation system for your garden
- Cut in half, drill some holes, and use them to start seeds in
- Cut off the top half and use as a funnel
- Use it as a vase. You could have kids decorate if for a craft project.
- Use them to store used cooking oil, so you can dispose of it properly
- Use the caps for paint for craft time
- Save the caps and color them red and black for checker pieces
- Use them to store small things like beads, paper clips, etc.
- Fly Trap
- Lava Lamps for Kids
- Really there are tons of crafting options (piggy banks and the like)
My only suggestion is to not refill them with something you plan to consume unless it is marked with the label PET (this is usually thicker plastics like soda and juice bottles). If you want a bottle you can reuse there are plenty available at just about every store.
If you have an idea/use for plastic water bottles, please share below and I will add it to the list!