Water Treatment


For questions about New Castle Water or about the Millwood Water Treatment plant, contact the Plant Manager

John Young
Phone: 914-944-0036



Raw Water is drawn by gravity from the primary source, the Catskill Aqueduct, through a siphon connection constructed through the top of the aqueduct. There is a standby connection to the Croton Aqueduct in the event of a Catskill Aqueduct shutdown.

The Rapid Mixers provide about one minute of high intensity dispersion of chemicals added to the raw water. The chemicals that can be added are alum, polyaluminum chloride, chlorine, caustic soda, polymer and potassium permanganate.

Flocculators provide about 30 minutes of controlled mixing of the water in three stages with coagulants that make particles such as clays, silts, viruses, bacteria, minerals, and algae stick together into large masses called floc particles.

Dissolved Air Flotation (DAF) removes the floc particles and clarifies the water. The DAF involves dissolving compressed air into a recycled water stream, and then releasing the air as microscopic bubbles that float the floc particles to the surface, where it is skimmed off. The clarified water is removed from the bottom of the DAF tanks. The detention time in the DAF units is about 25 minutes. The DAF process is used because it adapts better than other processes to the seasonal changes that occur in the quality of the raw water (variations from low to high turbidity, or amounts of particles suspended in the water) coming from the aqueducts New Castle uses.

Ozone, the strongest oxidizing agent among commonly used disinfectants, is the primary disinfecting agent. It is generated on site from the air and is injected into the clarified water in the ozone contact chambers, which provide about six minutes of effective detention time. By applying ozone after clarification, but before filtration, the ozone demand is minimized while any inorganic and organic oxidized material can be removed by filters. The ozone oxidizes any organic matter in the water, killing bacteria, viruses, algae, and microorganisms like giardia and crytosporidia.

Filtration is the final step in the physical removal of particulates and floc that have not been removed in the clarifiers. Filters, made up of 24 inches of anthracite coal on top of 12 inches of sand, strain the water and remove any remaining particles and floc. The filters are cleaned by backwashing with air and water, Depending upon the turbidity of the raw water, filters usually operate for 72 hours or more between backwashes. Well over 1,000 gallons of sludge is removed each day from the entire treatment system and pumped to a drying lagoon.

Final Chemical Treatment of the filtered water with a low dose of chlorine is done to maintain a residual of about 0.5 parts per million of free chlorine throughout the system. This assures the bacteriological quality of the water is maintained and prevents regrowth of any dormant bacteria in the distribution system piping. Caustic soda is added to raise the pH of the treated water from slightly acidic (less than 7.0) to slightly basic (more than 7.0). This optimizes the effectiveness of the orthophosphate corrosion inhibitor, which is also added to the water. The corrosion inhibitor reduces leaching of lead and copper from water pipes, particularly the individual service lines to residential buildings and plumbing within buildings. Fluoride is also added at this point.

The Treated Water Pumps lift water from elevation 335 feet in the filter control chamber of the treatment plant to a pressure level at the pumping station equivalent to an elevation of about 740 feet. The purified water is pumped out of the treatment plant into the distribution system. The 7.5 million gallon per day capacity treatment and pumping station sends the water through the recently relined pipe network on its way to remote pumping stations, storage towers and individual residences. The station includes four single-stage, 300 horsepower, centrifugal pumps with variable speed electric motors. The pumps are automatically controlled based on the water level in the system’s primary storage tank.

Quality control for New Castle’s water is assured by:

  • Computerized monitoring and feedback systems
  • Continuous water quality testing at all stages of treatment
  • Multiple backup systems: emergency generator, standby ozone generators, Croton Aqueduct connection, etc.

Water Supply History

In the early 1930’s the Town of New Castle, New York, developed a water supply from New York City’s Catskill Aqueduct with an aqueduct connection and pumping station. In the late 1950’s an additional supply was developed from Shaft Number 3 of the New York City’s Croton Aqueduct. The water from each source was disinfected with chlorine, but not filtered. During the 1980’s, the Town needed to expand and upgrade the existing sources of supply to meet increased demands. The New York State Department of Health also required filtration and in 1986, the federal Safe Drinking Water Act Amendments were enacted. The Amendments required the U.S. Environmental Protection Agency (EPA) to promulgate regulations requiring filtration of nearly all surface supplies. This led to EPA’s 1989 Surface Water Treatment Rule.

The Town’s Environmental Engineers & Scientists at Hazen and Sawyer, has been the consultant for the Town of New Castle since the 1950’s, when the Croton Aqueduct supply was developed. The firm provided planning, design, construction administration, and start-up services and operator training for the new supply from the Catskill Aqueduct at Millwood. Hazen and Sawyer proposed completely relining the antiquated water mains, building a new pump station to boost supply and constructing a modern water treatment facility using innovative technology. Under successive town governments, the pipe relining project began in 1984, the pump station construction began in 1988 and the treatment plant construction in 1990. The location for New Castle’s Millwood Water Treatment Plant was selected because of its proximity to both New York City’s Catskill and Croton Aqueducts. The new Catskill Aqueduct connection is designed as the primary supply with the existing Croton Aqueduct supply as the standby source.

The Town’s new Catskill Aqueduct connection and the Millwood Pumping Station was put into service in April 1992. The Millwood Pumping Station was converted into a filtered water pumping station in August 1993, when New Castle’s Millwood Water Treatment Plant was put on line.