When I was a kid, there was a storm drain in the gutter in front of the house. Water would flow in whenever it rained or when we washed the car. It seemed like an endless hole in the ground, covered by a large metal grate.

The grate could be removed, if you rolled a hot wheel car in there, but it was more fun to fish things out with a long string and some tape or chewing gum.

Sometimes we would drop fireworks in, to see what they would sound like, although we were always concerned that the fuse would be extinguished by the water we assumed was down there.

Sometime in the last ten years, "No dumping" signs began appearing on the curbs above storm drains here and in San Francisco. I bet they are all over the place.

In Sacramento they usually read "No Dumping, Flows to River", and in the San Francisco Bay Area, they usually say "No Dumping, Flows to Bay".

Like many warnings, these signs don't give much of an explanation.

It was many years before I really understood how the storm drain system works, so I thought I'd share what I've learned.

My sister Susan figured it out first.

Sue lives near Oakland, in the San Francisco Bay Area. She enjoys jogging around Lake Merritt, but was disgusted by the state of the lake. The water was often choked with trash.

She attended a meeting for clean-up volunteers, where she learned how rainwater fills the storm drains and pushes the trash in them into the local bodies of water, in this case Lake Merritt. 

Sixty storm drains, like the one to the right, flow into Lake Merritt. The system was built to make sure that streets aren't flooded when it rains. Unfortunately, the rain water picks up every kind of garbage on the streets and gutters, and washes it into the lake.

Cigarette butts, leaves, gum wrappers, straws, styrofoam peanuts and tiny Ziploc crack bags flow into these big grates. This is sometimes called urban runoff. In addition to these solid waste items, liquids like paint, anti-freeze, pesticides, bleach, soap and motor oil flow with the rainwater too.

I first found the Keep America Beautiful website when I was studying the herbalife signs in 2002. According to the KAB website, 18% of all littered items end up in waterways as pollution.

One beautiful Sunday in May, Tara and I went with Sue to check out the clean-up first hand.

Sue showed us one of the lakeside cleaning stations where the nets and garbage bags are stored.

Lake Merritt is the nation's oldest wildlife refuge. I know, I found that hard to believe too, but that is what their website says, so it must be true.

One of the first bits of garbage we snagged was this blue Cal-Steam Frisbee. This probably flew in from the lakeshore, not from the storm drains, although, if turned upside-down, it could easily have seated two mice, escaping from a secret underground laboratory.

Later that day, Sue showed us boxes of tennis and baseballs she has pulled from the lake.

There wasn't all that much trash in the water on the day we visited, which was good, but wasn't as satisfying as if we were clearing a real disaster.

One of the instances where people will litter is where litter has already accumulatedč, so removing every scrap of visible trash was a  goal that day.  We used the long nets to reach anything within about 10 feet of the wall.

Susan used her fancy fishing waders to snag some gunk farther out.

In this photo, the Glen Echo aerating fountain is visible. The fountains in Lake Merritt infuse oxygen into the water, compensating for all of the decaying leaves that flow into the lake. This helps the fish breathe and keeps the water from smelling rotten.

Sue also told us the story of how a volunteer once fished a one-kilogram bundle of cocaine out of the lake. A foolish dealer must have stashed it under the grate of a storm drain.

I guess they hid his dead body somewhere else.


Perhaps this colorful chart will help illustrate these two water systems, which, in most cities, are completely separate and never intermix: 

  • Handles small amounts of water and ick
  • Usually indoors
  • Smelly


  • Handles large amounts of rainwater
  • Usually outdoors
  • Usually odorless
Water in the sewer system is carefully filtered and cleaned in large wastewater treatment plants before being released into the environment. Water in the storm system flows into the environment without treatment.


The storm drain system has to be able to process millions and millions of gallons of water in just a few hours. Just one acre foot is equal to 325,851 gallons of water, so imagine how much rainwater can fall onto each square mile of a city.

I'm sure many people treat these gutters like bottomless pits. Because debris falls down into the drains, away from view, it is easy to treat them like garbage chutes.

The iron grating in front of storm drains has to be small enough to catch big pieces of litter, but if the holes are too small, it could quickly clog with leaves, resulting in a flooded street.

Warning signs on the storm drains could read "NO DUMPING, FLOWS UNCHECKED AND UNFILTERED INTO THE NATURAL WATER SUPPLY", but that's a little wordy. I think the most important bit of drain information is that the two waste-water systems are separate. 

Dumped fluids don't flow directly into our drinking water, but it does go directly into natural waterways. Maybe a river, a lake or the ocean. It is an easy bet that wild animals and plants are going to have to deal with whatever gets dumped in these.

I hope you enjoyed learning about storm drains!

If you want to learn more, check out these websites:

Lake Merritt foundation | Surfrider Foundation | Sacramento Stormwater

Montreal Urban Exploration - Raccoon Drain

čResearch by Keep America Beautiful, Inc., has found that people litter because:
  • They feel no sense of ownership, even though areas such as parks and beaches are public property.
  • They believe someone else—a park maintenance or highway worker— will pick up after them.
  • Litter already has accumulated.

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Last updated May 21st, 2003.

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