You’ve heard the phrase. Here’s an explainer for what it means.

A source of drinking water for upwards of 13 million people, the Delaware Watershed is imperative to Americans as far north as New York’s Schoharie County to the southern beach towns of Delaware.

So pour yourself a cold glass of tap and learn more about the 13,500 square miles that comprise the Delaware Watershed.

Watershed 101

A watershed is an “area of land draining to a particular stream,” according to the Delaware River Basin Commission, which says the term is essentially synonymous with “basin.”

This video from Caring for Our Watersheds explains more.

A tributary is a stream or river that flows to a larger river and does not directly drain into the ocean. The Delaware River is a mainstrem, or the parent river that’s fed by the tributaries. An estuary is the section of the river where the tide flows in and out, and fresh and saltwater mix.

Let’s get into the Delaware Watershed

• The Delaware River is 330 miles long.
• It runs from Hancock, N.Y., where the East and West branches meet, to the Delaware Bay.
• 2,000+ tributaries flow into the Delaware River.
• The Schuylkill and Lehigh rivers are its largest tributaries.
• From Hancock, N.Y. to Trenton, N.J., the river is non-tidal and freshwater.
• The portion of the river that runs from Trenton to the Delaware Bay is known as the Delaware Estuary; it’s tidal and its salinity levels vary.
• The Delaware River is the longest un-dammed U.S. river east of the Mississippi River.

How large is the Delaware Watershed?

The river basin is 13,539 square miles, a massive area that’s equal to about 6.5 million football fields. The Delaware Bay makes up 782 square miles of the basin and land in New York, New Jersey, Pennsylvania and Delaware constitute the rest.

• The watershed includes 838 municipalities in 42 counties. Here’s a full municipality list from the DRBC.
• With 6,422 square miles of the basin in Pennsylvania, land in the Keystone State accounts for 50 percent of the basin’s total land area.
• A river mileage system is used to describe stream locations. Mile zero denotes where the Delaware Bay meets the Atlantic Ocean & river mile 330.7 represents the mainstem starts in Hancock, N.Y.

What you’re drinking

DRBC data from 2016 shows at least 13.3 million people, including about 5 million people in New York and North Jersey located outside the basin, get their drinking water from the Delaware Watershed. Other organizations put the figure at closer to 15 million, or nearly 5 percent of the U.S. population.

The water, thankfully, is not piped directly from the river to our faucets at home. An extensive treatment process takes place to ensure the water is safe for consumption. This infographic from the Philadelphia Water Department explains what happens before you turn on the tap and after you flush the toilet.

That’s not all…

The Delaware Watershed is responsible for more than drinking water. Of the roughly 6.6 billion gallons of water drawn from the basin daily, more than half is used for thermoelectric power generation. It also directly supports other industries like tourism and agriculture, generating an annual economic impact of $21 billion.

Thanks to its ports, the river basin has an even deeper effect on the economy. In 2019, more than 90 million tons of cargo passed through the Delaware River Port Complex, which includes several ports in Delaware and New Jersey, as well as the Port of Philadelphia, according to the Maritime Exchange for the Delaware River and Bay. That heavy load translates to $85.6 billion in business and personal revenue each year.

Sources: The Delaware River Basin Commission; the Coalition for the Delaware River Watershed; the Philadelphia Water Department; the Delaware River Port Authority; and National Geographic.

Lead support is provided by the William Penn Foundation.

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Alison Burdo is a project manager with Green Philly, focusing on the development and execution of its coverage of the Delaware Watershed. A Philadelphia-based journalist for the past seven years, Burdo most recently supported the launch of the Initiative for Better Gun Violence Reporting. Her experience includes reporting exclusive, enterprise stories on the 2015 papal visit and the 2016 Democratic National Convention; leading an investigation into the epidemic of unsolved missing persons cases; and regularly breaking news related to Philadelphia's precedent-setting soda tax. View all posts by Alison Burdo