Journey to the Tap: How does NYC Treat Its Water?
The city’s water supply system has 19 reservoirs and 3 controlled lakes that all result in the very same thing: high-quality drinking water flowing straight from your tap.
By now, you may know that our water supply system is actually made of three separate supply systems:
- The Catskill and Delaware Supplies—located in Delaware, Green, Schoharie, Sullivan, and Ulster Counties
- The Croton Supply—located in Putnam, Westchester, and Dutchess counties
The water that each system produces has unique characteristics and requires different types of treatment before it enters the city’s distribution system.
The Catskill/Delaware System
The quality of the water from the Catskill/Delaware system is so high that it enables NYC to have a distinction that only 5 large cities in the US can lay claim: we aren’t required to filter that drinking water as part of its treatment. We are issued what is known as a Filtration Avoidance Determination—more commonly known as the FAD—so we just treat this water with two forms of disinfection (chlorine and UV light) to reduce microbial risk.
The Croton System
The Croton system, on the other hand, does require filtration. This system typically supplies about 10% of our daily drinking water and provides the entire system an important level of flexibility that is crucial during times of drought or operational changes. Croton was our very first water supply and like any good Day 1, Croton is always there when we need it.
Before it makes it to disinfection, water from the Croton system takes a little trip through the Croton Water Filtration Plant. At the plant, chemicals are added to the untreated water in a process called coagulation. The chemicals added to the water cause particulates in the water to bunch together and become larger particles called, “floc.”
Next, air bubbles are injected into the water to float the floc to the top, where it is then skimmed off in a process called dissolved air floatation. As the last step in the filtration process, water flows through a bed of sand to remove any remaining particles.
Both water systems are subject to treatment with chlorine, UV light (both for disinfection), fluoride (for those teeth), sodium hydroxide (to raise pH and reduce corrosion in household plumbing), and food grade phosphoric acid (to help prevent pipes from leaching chemicals into the water). After that, fresh, clean water is delivered straight to your tap.
Cheers!
