Plastic bottles are used once and tossed, yet they're durable, waterproof and free. Most people never imagine the second life hiding in their recycling bin.

Design a second-life use for discarded plastic bottles. Study who is affected, dig past the obvious symptoms to the real root causes, and design a solution that could actually work in the real world. There is no single correct answer — what matters is the quality of your thinking, the stakeholders you consider, and how clearly you justify your chosen direction.

• Who is most affected by this problem, and how did you account for them?
• What is the single biggest risk to your solution working?
• Which assumption, if wrong, would break your whole idea?