The Washington region is growing — a metropolis of nearly 6 million people where area officials are pressing to build another 320,000 homes by the end of this decade.

And with that growth comes an increasing, largely unregulated problem: Salt. Lots of it.

Paved streets, sidewalks and parking lots need de-icing in winter, with the sodium chloride in road salt running off intostreams. Washing machines drain sodium-containingdetergents and industrial firms discharge sodium-laden water into wastewater systems, which already treat the human waste of a society addicted to salty foods and drinks.