Famed inventor Dean Kamen has created an efficient, inexpensive water purification system that could help a billion people worldwide who don't have access to clean water. The system is more efficient than other water purification systems because it recycles waste heat used in the distillation process.
At $2000 per unit, the systems can provide enough clean water for about a hundred people. While that's impressive, it's unlikely that people in the poorest parts of the world—where these systems would be most needed—can afford to spend two grand for every thousand people in the area. Maybe some philanthropic organization like the Gates Foundation will come along and help out, but until then Kamen's invention is just something for him to get clean water in his lab.