Wastewater is ubiquitous. It pollutes coastal waters from the temperate zones to the tropics — and its threat reaches beyond underdeveloped countries. In fact, very few places have managed to avoid discharge of untreated wastewater into surface waters. A recent review of wastewater pollution impacts on coral reefs found that of the 108 coral reef geographies with human populations, 104 had a documented wastewater pollution problem (Wear & Vega Thurber, 2015). Approximately 31% of the world’s salt marshes are exposed to high levels of wastewater pollution (Wear et al., 2021).

Wherever you have people, you are likely to have some sort of wastewater problem. Approximately 80% of the world’s wastewater is discharged untreated into surface waters (UN WWDR, 2017) with some places having even higher discharge rates (e.g., the Caribbean, with 85%; Diez et al., 2019). In New York City, even a light rain triggers a combined sewer overflow system, which discharges an average of 27 billion gallons of wastewater and stormwater directly into New York Harbor annually (NYSDEC, 2008). In Hawaii, more than 88,000 cesspools discharge an estimated 53 million gallons of untreated wastewater into the groundwater each day (Hawaii DHEM, 2018). This does not include leaky septic tanks or sewage spills from inadequately managed treatment facilities. In total, the U.S. discharges about 1.2 trillion gallons of untreated wastewater into coastal waters annually (EPA, 2001). This problem is only getting bigger as the population grows, and people move to coastal cities. Already about 40% of the world’s population lives within 100 kilometers of a coast.