A few months ago, I was driving with a young student (about 21 years old) who, before I knew what happened, threw a plastic water bottle out the window.

We were in heavy traffic and there was no way I could stop or turn around. I looked at him in disbelief and asked him why he just did that. Nonchalantly, he responded, “What difference does it make?”

“It makes a huge difference in so many ways,” I said, and I proceeded to tell him about limited natural resources and the journey of stormwater.

Have you ever wondered what happens to the fast-food bag, cigarette butt or other trash simply thrown out the window or left in a parking lot? Street sweepers don’t have a big dustpan that follows them around after all. They merely sweep trash away from the gutters.

During heavy rain storms, or after big snow melts, when the ground cannot soak up the water fast enough and it all runs down to the street, water in the streets picks up the trash and carries it from the street stormwater drain to the city’s stormwater treatment facility – that is, if the city has a separate sewer system.

Some cities like Kansas City have a combination of both “separate” and “combined” sewer systems. Most smaller area cities have either a separate, or a combined sewer system dependent on the age of the city.

In a separate sewer system, stormwater (water from outside, from rooftops, streets, sidewalks, parking lots, and other impervious surfaces) and wastewater (water from inside houses and buildings) is collected in two different pipes. The wastewater is routed to a wastewater treatment plant, and the stormwater flows directly to nearby rivers and streams without treatment.

According to the Kansas City Water Service website, combined sewer systems are found in the oldest parts of Kansas City, some dating back to 1863 are still in use today. Combined sewer systems are typical for old cities. A combined sewer systems collect stormwater and wastewater in the same pipe. After collection these mixed waters are then routed to a wastewater treatment plant.

However, during periods of moderate to heavy rainfall, like we experienced last week, sewer systems can reach capacity, and overflow. At this point, the pipes reach their overflow and the mixed water (wastewater and stormwater) is discharged into the nearby streams and rivers.

Hopefully, there’s a better understanding of how throwing trash out of car windows really does matter. Why building a parking lot or sidewalk upon every piece of ground really does count. And how it all adds up.

Perhaps most of all, we can do something about it – one little step at time. Put a trash bag in our car and when it is full, throw it away in a trash can.

Lynn Youngblood is the executive director of the Blue River Watershed Association in Kansas City, a residential energy client service coordinator certified by the National Energy Retrofit Institute, and a past nature center manager with the Missouri Department of Conservation.