by Ryan Brenner

Rain in the City can be brutal: empty cabs are impossible to find, the subway is delayed, umbrellas are untamable, and raw sewage flows directly into our waterways. Yes, you read that correctly. When enough rain falls, untreated sewage mixed with polluted storm water flows directly into bodies of water across the City as combined sewage overflow (CSO). How often does this happen? Is raw sewage flowing into New York Harbor right now? Under New York law, you have the right to know. Chances are, though, you do not. Rest assured, you did not miss an advisory or fail to notice a pipe spilling out sewage. You likely do not know whether a CSO event is occurring because New York City’s current alert system is slow, uninformative, and needs to be replaced.   

First, why is this happening? New York is an old city with old infrastructure. Sewage systems were initially designed to combine gray water (showers and sinks), sewage (toilets), and storm water (rainwater that collects in storm drains) into one collection system. Under normal conditions, this “combined sewage” flows through a wastewater treatment facility where solids, pathogens, and chemicals are removed before the treated water is returned to a body of water. When too much rainwater accumulates, the system collects more than it can process. Since the combined sewage needs to go somewhere, the collection pipes are designed to intentionally “overflow” into a body of water without first passing through the wastewater treatment facility.

Dumping untreated human waste into our bodies of water is just as bad as it sounds. According to the most recent State of the Estuary report, CSO events introduce more pathogens (the microorganisms that cause such diseases as typhoid, cholera, and hepatitis) into our waterways than any other source. The aptly named Swimming in Sewage report adds that CSO events also introduce carcinogenic chemicals and cause “dead zones” that disrupt fisheries.

Despite these risks, CSO events occur frequently throughout the City. This is because as little as one twentieth of an inch of rain is all that it takes to cause a CSO event. On average, that translates to at least one CSO event every week. With 460 discharge sites across the City, this means over 27 billion gallons of sewage and storm water each year flow directly into the harbor without any treatment.

Unless you are planning on avoiding water altogether, it is critical that you know when a CSO event is occurring. If CSO is flowing into a body of water, you should avoid contact (e.g. swimming, boating, fishing, etc.) with that body of water (anywhere that could possibly overflow is required by law to have a warning sign). However, because the City does not draw its drinking water from local bodies of water, CSO events will not affect your tap water.

Knowing when a CSO event is occurring can also help you reduce the impact of the event. For example, if you wait to do laundry and use the dishwasher, take shorter showers, run the tap less, or even flush only when necessary, you will reduce the volume of sewage flowing through the system and potentially offset the additional rainwater causing the overflow. Constant reminders can also serve as a motivation to invest in longer-term solutions like green infrastructure that absorbs or slows rainwater runoff.

The City has just started a pilot alert program in Brooklyn, but the scale is small and advertising is limited. We need to let the City know that this is an important issue that we want to be informed about. Though critics may say that CSO events are insignificant and that warning the public is a waste of time, CSO is hazardous to public health and the environment and we have a legal right to know when it is happening. Let the City know that you care by emailing the pilot program,, and asking for the alert system to be offered to a wider area. Addressing this issue would go a long way towards protecting our waterways and would also help make rain in the City a lot less brutal.