Stormwater runoff, the rain or snowmelt that “runs off” ground and other hard surfaces, is as old as the first rainfall. What’s new is the impact human progress makes on this formerly “natural” event. The coming collision between runoff and humans may soon be playing at a courthouse near you.

The issue is hardly novel. Ownership conflicts make up much of the court’s business. But who owns stormwater? Much less, who cares? Usually, the people who care are the ones awash in stormwater. Their numbers are growing.

Consider this scenario enacted at least once a hurricane season. A neighbor’s tree falls into your yard, but their insurance agent (even your insurance agent!) say it’s your job to clean it up because an act of nature put it on your property.

Let’s apply that same premise to stormwater. If my neighbor builds a deck that then sends runoff cascading into my basement, whose job is it to clean up the water, much less prevent a repeat flood? Rain is an act of nature, but what about that deck?

How about public property? Your town built a big new school complete with a one-acre parking lot. The parking lot sheds 16 times more water than the one-acre meadow it replaced, and now the runoff overwhelms the closest storm drain. That causes the road in front of the largest, hotly recruited, new employer in town to flood. Who owns that stormwater? The school board? The school contractor? The public works department? Or the business that owns the flooded property?

Stormwater quantity is just half the equation, though. Runoff quality is often poor, given all the oil, brake dust, dog poop, and pesticides it gathers en route to the storm drain. The untreated water goes to creeks, streams, sounds, and bays full of living creatures.

Imagine you harvest shellfish for a living. The state closes shellfish beds as a precaution after every major rainfall. Why? The shellfish, who eat by straining water for nutrients, also pick up the pollutants. People get sick if they eat these shellfish, but you lose money when they can’t be harvested. Who owns the stormwater that put you out of work? People living upstream? The local government? You?

While fictional, these scenarios represent questions being asked more frequently. If the primary source of water pollution is stormwater, and the primary source of stormwater pollution is people, do we all own the stormwater? We all benefit from clean water, but stormwater impacts are more local. Given the pace of development, they’ll be more frequent, too.