Person with umbrella standing in a flooded street.January 1, 2023 marked more than just the beginning of a new year for Bay Area residents, bringing intense floods and some of the wettest days to cities like San Francisco. On New Year’s Eve, a powerful atmospheric river soaked Northern and Central California, knocking out power, trapping people in their vehicles, and forcing the closure of highways and other submerged roadways. Downtown San Francisco measured 5.46 inches of rain, making this its second wettest day in over 170 years. For many Bay Area cities, this flooding brought many challenges, however in the case of San Francisco, its unique stormwater system brought another challenge—overflowing raw sewage. During these storms, raw sewage from San Francisco overflowed into creeks, the bay, and city streets. In response to this, Eileen White, executive officer of the San Francisco Bay Regional Water Quality Control Board, released the following statement to SF residents: “Don’t jump in puddles. Especially in San Francisco — you want to be careful that there (could be) sewage in that.”

But how is raw sewage such a big problem during heavy storms in San Francisco? This ultimately comes down to San Francisco’s unique stormwater system, which combines raw sewage and stormwater runoff into a single system. This system is backed by the San Francisco Public Utilities Commission (SFPUC) who says this is a greener option that allows for stormwater to be treated the same way as sewage before it enters the bay. In other Bay Area cities without this design, stormwater discharges directly into creeks, rivers, and the bay without any treatment, meaning that any pollutants picked up by the stormwater will go straight into natural water bodies. These pollutants include trash, construction debris, automotive fluids, pesticides, fertilizer, industrial chemicals, petroleum residue, coal dust, and soot. These pollutants can create harmful algal blooms and dead zones with less oxygen in the water, impact fish health, and lead to these aquatic species being unsafe to eat.

Understanding the dangers of untreated stormwater, it seems clear that San Francisco’s combined stormwater and sewage system is beneficial as it ensures that all water being discharged into natural water bodies has gone through thorough treatment. However, three factors stand in the way of this system being truly beneficial: the fact that San Francisco’s stormwater system is already prone to flooding, the city is more vulnerable to system wide backups, and the effects of climate change. Particularly in low-lying areas, San Francisco’s stormwater system is prone to flooding, specifically flooding that contains raw sewage. Coupled with climate change, where storms are expected to get more intense, this problem will only get worse. What is disappointing about this issue is the extreme lack of funding and interest in these flood-prone communities. Even before the full effects of climate change were accounted for, sewage overflow was already causing damage to low-lying neighborhoods in the 1960s. Dating back to the 60s up until now, projects to improve the city’s sewer system have been proposed then discarded, with no real change being made. With climate change leading to more intense and prolonged storms, San Francisco is only more vulnerable to systemwide backups. Heavy flooding, like what was experienced around New Year’s, leads to overflow of stormwater systems, sewage systems, and wastewater treatment plants, where recovering these systems and returning back to normal levels take time and many other resources.

It is clear that San Francisco’s stormwater system has both its pros and cons. However, coupled with the effects of climate change, one could argue that the cons outweigh the pros and that this current system is in dire need of repair. However, that is much easier said than done. Experts say that a complete overhaul of San Francisco’s current system is practically impossible not only due to the cost, but the amount of disruptions it would cause to all those who utilize public roadways. Because everything in the system is underground, the task of physically upgrading San Francisco’s stormwater system is a monumental one, with experts stating that at this point, there’s no way to change it. With a complete restructuring of the city’s entire sewer system being not feasible, there are smaller fixes that can be done. Said fixes would help to make the city less flood prone and include repairs and utilization of green infrastructure. Significant repairs and improvements to the current system would keep water flowing even if there is extreme flooding and investing in green infrastructure like rain gardens could keep runoff from entering the sewers in the first place.

Communal efforts are also pushing to reduce the effects of stormwater, including those of Baykeeper. Baykeeper is a team of lawyers, scientists, activists, and community members who hold industrial facilities accountable when their harmful chemical byproducts discharge into the bay, advocating for stronger regulations on trash and other common stormwater runoff pollutants. On a much smaller scale, San Francisco also has an Adopt-a-Drain program, where individuals can select one of the city’s 25,000 storm drains and pledge to keep it free of debris and pollutants. This not only reduces the risk of flooding by minimizing pollutants and trash that clog and go down the drains, but it also fosters community engagement and a sense of purpose. Although these smaller efforts have made an impact, a question is raised: is this enough? Community engagement and holding polluters accountable are certainly important, but when San Francisco is faced with another set of heavy storms and subsequent flooding, will there be significant change?

As individuals, it is our responsibility to continue these efforts, no matter how small, and advocate for change on a larger scale. Taking climate change into account and understanding that storms will only become more intense and prolonged, it is up to us to make a change. Hopefully, the consequences of this winter’s heavy storms will be a wakeup call, and we can start with our own individual efforts to reform San Francisco’s urban water systems.


Cappucci, M., & Brasch, B. (2023, January 2). Northern California sees historic deluge as atmospheric river slams state. Washington Post.

Duggan, T., & Hao, C. (2023, January 18). Sewage overflows into San Francisco Bay and city streets during storms. San Francisco Chronicle.

Shultz, A. (2023, January 12). Civic programs can’t save SF’s antiquated sewers from flooding. SFGATE.

Stopping Stormwater Pollution in the Bay. (2021, December 14). San Francisco Baykeeper.