Keeping roads safe in the winter is a high priority for cities throughout the country. Salting the pavement is the cheapest way to do that. When a salt crystal dissolves, it releases its component ions—sodium and chloride—which both bond with water molecules, making it more difficult for them to join to each other and thereby freeze. The problem comes from all that chloride and salt run-off. The chloride gets into our water supply and poisons fish. The salt burns vegetation and contaminates soil, as well as corroding cars and bridges. But it's cheap. Ten times cheaper than effective alternatives. And when a city of 2.5 million people needs 135,000 tons of it, that's a significant cost difference.