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Where Does Water Go After it Goes Down the Drain?

Where does water go after it goes down the drain? | Iowa DNRWhether it’s rainfall from a summer storm washing over land, or wastewater from your household, all water heads downhill, often through a drain.  

When it rains, each tiny raindrop is powerful, smacking bare ground like a mini-bomb, dislodging soil and tossing it into the air. Whether in a farm field or yard, it can carry soil particles into nearby ditches or streams. Often, rainfall picks up nutrients, pesticides, livestock or pet waste, and harmful substances that runoff from roads, roofs and parking lots.

In many cities, rain flows into storm sewers, beginning an underground journey, down the drain and to the stream. So, be careful, since anything you put in your yard, street or storm drain will flow directly to a river or lake in your community. Protect those favorite spots and the fish, crayfish and aquatic insects that live there by keeping household chemicals, cleaners, paint, lawn care and similar products out of storm sewers.

Flush it or dump it. Dirty water from your bathtub, sink, washing machine and toilet takes a similar journey, down the drain. Although nearly 100 percent water, wastewater contains potentially harmful substances including suspended solids such as human waste, food scraps, oils, chemicals, soaps; and industrial byproducts. In the U.S., the 1972 federal Clean Water Act requires sewage to take a wastewater treatment tour before flowing back into a stream.

In rural areas, wastewater treatment is also required. For many homes, that’s an individual septic system, an underground tank where most solid materials settle out. Liquids then flow into a leach field where holes in buried pipes allow liquids to seep into the soil, a natural pollutant treatment system that protects groundwater.

In a city, household drains connect to a larger pipe that carries wastewater into the city’s underground collection system of sanitary sewers. As wastewater from homes, businesses and industries collects, sanitary sewer pipes get bigger and bigger as they near the wastewater plant. Sometimes, wastewater must be pumped uphill on its way to the city’s wastewater treatment plant.

Cities must meet water quality standards, but they have different options to remove pollutants from wastewater before returning it to the environment. Some communities use primary treatment to screen and settle out about 40 or 50 percent of the solid material, like fecal matter and toilet paper. All communities use a secondary treatment technology, which depends upon bacteria to break down organic matter like food particles or fecal material, and final settling. This process removes up to 99.9 percent of coliform bacteria. The final treatment step kills a significant amount of the remaining disease-causing organisms with chlorine or other disinfectants. An increasing number of communities use more advanced treatment to further reduce pollutants like nutrients.

Once the water is clean enough to meet discharge standards, it flows into a nearby stream or lake, where fish and other aquatic animals can use it. Humans, too, may re-use the water, pumping it up, testing it and often treating it so it is safe to drink, then pumping it to your house.

Hazardous chemicals can harm the bacteria used in wastewater treatment plants. So, again, be careful what you pour down the drain. Household chemicals – from extra shampoo to medicine, fertilizer or pesticides – can interfere with wastewater treatment. And, they might end up in your local streams and lakes. Please take them to a Regional Collection Center.

What to flush? Add only toilet paper to your drain. Grease, diapers, baby wipes, personal hygiene products and rags can clog pipes, causing untreated sewage to back up into your home or overflow at a manhole, then run across yards. These products are garbage, not drain material.

For ideas on how you can be eco-friendly at home, check out our Earth Day Every Day and In Your Own Backyard boards on Pinterest.