Stormwater 101


Learn the basics of Stormwater

Stormwater badge icon

What is stormwater? 

When rain, snow, or another type of precipitation hits a surface, it becomes stormwater. In natural landscapes, stormwater gets soaked up into the ground or falls directly into waterbodies. However, when rain or water hit hard surfaces like pavement, sidewalks, parking lots, asphalt roadways, and roofs it creates stormwater runoff. On its journey, stormwater picks up and transports many of the pollutants it encounters, which are NOT treated before entering a manmade infrastructure of storm inlets and pipes before draining directly to the rivers, streams, and creeks. These pollutants include sediment, pet wastes, pesticides, fertilizers, automobile fluids (such as oil, gasoline, and antifreeze), yard wastes, cigarette butts, litter, and more. By carrying all these different kinds of pollution into our waterways, stormwater runoff itself becomes a pollutant!  As a developed urban area, the City of Annapolis is especially susceptible to stormwater runoff because of the large amounts of impervious surface.

Storm drains (like those found along curbs) do not go to wastewater treatment plants. Water entering storm drains flows untreated into streams, creeks, rivers, ponds, wetlands, lakes, the bay and ocean. Stormwater devices can be installed to capture and treat the stormwater runoff prior to reaching the local waterways.

The stormwater conveyance system channels rainwater flow from sidewalks, streets, curb & gutters to storm drain inlets, underground pipes, outfalls to local waterways.

Image showing the parts of the stormwater conveyance system

What is an Impervious Surface?

An impervious surface is any surface which has been covered with a layer of material that seals off the soil such as pavement, sidewalks, parking lots, asphalt roadways, roofs, and even semi-pervious surfaces such as compacted clay and gravel.  This prevents rainwater from naturally soaking into the ground and reconnecting with groundwater. The impervious surface causes excess water to runoff and flow into the stormwater conveyance system then to local waterways through a stormwater outfall.

Impervious Surface
  • Stormwater runoff is the fastest growing source of pollution to the Chesapeake Bay (Chesapeake Bay Foundation).
  • Pollution carried by stormwater damages fisheries and habitat of plants and animals that depend on clean water for survival
  • Limits recreational uses of water bodies by making them unsafe for wading, swimming, boating and fishing.
  • The amount of impervious surfaces has an impact on water quality.  

HOW CAN YOU HELP!    Here are some tips...

Yard Trim Collection


When not disposed of properly yard waste flows down storm drains causes drain and pipe blockages, then acts as a pollutant by adding excess nitrogen and phosphorus into aquatic systems as it decomposes, can cause algal blooms which deplete oxygen levels causing problems for aquatic wildlife.

Fact:  56% of phosphorus in urban stormwater comes from yard trim.

Best Practices

  • Collect your yard trim in a Green City Cart, lawn paper bags, or a container of your choice marked with an "X". Learn more about Yard Trim Collection
  • Leave grass clippings , they breakdown quickly, form an organic soil layer which increases stormwater infiltration.
  • Consider composting or mulching yard trim
  • Never rack your leaves to the street.
  • Make sure the storm drain inlet is clear of any debris.

Pet Waste

Image does not exist

Problems with leaving pet waste.

Pet waste can not be used as a fertilizer as it is to acidic.  

It also can contain harmful bacteria and parasites. 

Poop doesn't decompose very fast, instead rainwater can move it down storm drains into waterways.

Causes problems for aquatic plant and animal communities.

Best Practices

  • Bag It, Toss It in the trash.

Pesticides, Herbicides & Fertilizers, Household Hazardous Waste (HHW)

Image does not exist

See how these impact stormwater:

Fertilizer runoff causes excess nutrients in waterways creates algal blooms harmful to wildlife and humans

Pesticides become a stormwater pollutant that impact non-pests including aquatic insects that are an important food source for wildlife and bioindicators of stream health

Herbicides that runoff can harm non-target plant species important to stream bank stabilization, filtration, and local wildlife

Best Practices

  • Invite natural pest predator into your garden such as lady bugs
  • Create DYI products with non-toxic ingredients
    • pesticide with soaps, spices, essential oils, and garlic
    • herbicides with dishsoap, salt, vinegar
    • fertilizer with left over yard trim and food scraps
    • cleaning products out of non-toxic ingredients like lemon, baking soda, and vinegar 

If you use chemicals read label and apply accordingly and sparingly. Purchase non-toxic products when possible 



Litter isn't always purposefully done, it can occur accidently by blowing out of overfilled containers.  When litter is left on the ground, sidewalk, or street it can find it's way into the storm drain or waterways.  This can cause:

  • storm drain inlets and pipe blockages
  • wind and water break down plastics and other litter into small pieces which can be mistaken for food by aquatic wildlife
  • get stuck on storm drain grates partially blocking stormwater flow can cause local flooding 

Best Practices

Vehicle Maintenance

Image does not exist

Best Practices

  • If possible take the vehicle to an facility equipped to do this work.
  • When doing vehicle maintenance at-home: 
    • perform maintenance in a covered area
    • use funnels to prevent fluid spills
    • absorb any spills with sawdust or cat litter and sweep into the trash
    • store car fluids safely and dispose of properly according to the label
  • While waiting for repairs place a pan under any drips or leaks so the material can be properly disposed of.  

Washing Your Car

Image does not exist

Best Practices

  • Buy or make a sulfate-free biodegradable soap
  • Wash car on the lawn instead of road or driveway to prevent cleaning products from going down the storm drain
  • When possible take your car to the car wash where water is treated after cleaning

Water Without Waste

Image does not exist

Conserving water when working outdoors can reduce the potential for contaminants for getting in local waters.

Best Practices

  • Adjust sprinklers so that they don't water paved surfaces.
  • Don't water in the heat of the day.  Watering early in the morning or in the evening minimizes the water lost to evaporation.
  • Consider using a slow-watering technique such as drip irrigation or soaker hoses.  They are considerably more effective than sprinklers at getting water where it's suppose to be.

Rain Garden

Image does not exist

A rain garden is a landscaped area specially designed to collect and treat rainwater runoff in your yard.  These might be regulated stormwater practices? Maintaining them is your responsibility. 

Best Practices

  • Use native plants

  • Water plants upon establishment 

  • Keep dense vegetation in your rain gardens 

  • Don’t use fertilizer 

  • Occasionally remove the top layer mulch if there is a lot of sediment accumulation. 

  • Don’t fill in your raingarden or other stormwater practices. 

  • Don’t run large equipment over your rain garden or other infiltration practices as it will compact the soil 

Green Gardening

Image does not exist

Achieving a lush green lawn, beautiful flowers, and hearty summer crops are great gardening goals. While lush lawns help soak up the rainwater and prevent soils from eroding.  It could also be harmful to the local waters.

Best Practices

  • Fertilize sparingly
  • Mow high and leave grass clippings on lawn
  • Hand pick weeds when possible, if must treat weeds then spot treat them.
  • Set your mower to 3" or higher.  This encourages deeper roots that increases water absorption and prevents runoff/ erosion

Sweep Up

Image does not exist

Anything that's lying on pavements or sidewalks is more easily washed by stormwater down storm drains.  This could cause the storm drain to become clogged and cause flooding.

Best Practices

  • If lawn chemicals or yard debris get on sidewalk, driveway, or pavement sweep them back into the lawn or pick it up to keep it from washing into storm drains.
  • Grass clippings and excess leaves don't belong in our storm drains, streams, and rivers.
  • Sweep, DON'T hose, the driveway

Report any illicit discharges, dumping, or spills into storm drain inlets, creeks, or streams

Have a Problem?

Use "Report A Problem" to let us know about City issues.

24/7 Texting Information

Text My Gov Icon