RALEIGH, N.C. — One afternoon last month, artist Sarahlaine Calva kneeled on the sidewalk above a storm drain along John Chavis Memorial Park, southeast of downtown, painting a mural of giant flowers in vibrant colors.

"The message is subtle, but when people are walking by, I want them to get it," said Calva, wearing ripped jeans and paint-splattered Vans. "A lot of people make the connection. One guy said he wanted to plant a garden nearby to make [the area] look nicer."

That connection – between storm drains and the health of local waterways – is becoming clearer as cities across the country call attention to the drains with murals and signage to reduce water pollution and educate residents about the harms of using them as trash receptacles. "Only rain down the drain" is an increasingly common refrain in municipalities that have launched awareness campaigns around stormwater runoff – rainwater or melted snow that doesn't soak into the ground but rather flows over pavement and picks up pollutants before it reaches the nearest stream or lake. (When the water soaks into the ground, the soil filters it before it reaches aquifers or streams.)

Runoff has become one of the leading causes of water pollution. In recent years, a number of cities have invested in marking storm drains, which often means attaching decals to the drains, explaining that they're only for rain, not for trash or dumping. Raleigh is among the cities – including Richmond, Virginia; Lubbock, Texas; Lafayette, Louisiana; and Fayetteville, Arkansas – that have taken the next step in bringing awareness to the public by creating murals on and near the drains.

"When it rains, the stormwater runoff goes directly to our waterways," said Kristin Freeman, a spokeswoman for the city of Raleigh's stormwater management division. "We don't want trash, grease, oil, wastewater or pet waste to go into the drain, because it's not treated like drinking water is."

Through the art, Raleigh's stormwater management division wants to teach residents – who sometimes still pour liquids like cleaning products, motor oil and paint down the storm drains – that what goes down the drains directly impacts the health and quality of lakes and streams. It also affects the wildlife that live there and the humans who use the water for recreation. In Raleigh, the main creeks affected are Walnut and Crabtree, which lead to the Neuse River.

Known for her murals on unusual surfaces (she's painted a basketball court, piano, car and bus shelter), Calva was selected by city officials to paint murals at five drains, a project that began last September. The city, which sets aside 1% of municipal construction funds for public art, selected drains in areas of Raleigh with heavy pedestrian traffic that are experiencing significant water pollution issues. Calva's art is created in a cartoonish style that includes abstract fish, plants and water droplets, indirectly telling the storm water story.

The city is relying on social media, staff education and volunteers to further convey the message. An outreach coordinator visits schools and sets up at community events to demonstrate what happens to rainwater and runoff, discuss how pollutants impact the environment and explain how residents can help. In the fall, the parks department held a Pop-Pup Dog Park near the Nash Square Park storm drain mural, during which the city distributed pet waste bags and educated residents about the importance of picking up after their dogs.

Freeman said the stormwater management staff will track the success of the murals during their life span; she predicts that pedestrian traffic and weather will wear them away within a couple of years. Several times a year, the city takes samples from 18 stream sites, studying the health of the water by measuring nitrogen, phosphorous, E. coli and pH, among other variables. It's still too soon to know whether Calva's colorful flowers and raindrops will make a difference for the fish in Raleigh's waterways. For now, Freeman said, success is being measured in understanding and exposure to the artwork.