The main problem I see with them is people's perception about what porous pavements do. Great, water goes through them... and then what? The ground underneath t

The main problem I see with them is people's perception about what porous pavements do. Great, water goes through them... and then what? The ground underneath the pavement is not some unlimited sinkhole for water. The ground table can and does fill up. Then it doesn't matter how porous your pavement is. Trees, grass, wetlands, etc, do better in part because they are preventing the water from leaving. They pool water in small puddles, they absorb water, leaves have water sit on them, etc.