Nashua has approx. 400 miles of municipal sewers that range in pipe diameter from 6 inches to 108 inches. This extensive network of sewer pipes ends up, eventually, at the Wastewater Treatment Facility at Sawmill Rd.

Of that 400 miles approx. 25% (or 100 miles) is combined sewer.

• Separated sewers are separate pipes for sanitary sewage and storm water with sanitary sewage going to the Wastewater Treatment Facility for treatment, and storm water from catch basins and headwalls discharging into natural runoffs, i.e., rivers, streams, detention ponds, etc.
• Combined sewers are one pipe collecting both sanitary sewage and storm water runoff with the final destination of treatment at the Wastewater Treatment Facility

There are 9 CSO (Combined Sewer Overflows) regulating structures in operation. A CSO is, basically, a manhole that can divert runoff through pipes to rivers during extreme rainfall conditions.

According to the most recent study (Camp, Dresser & McKee, 1995), the Nashua sewerage system services approximately 75 percent of the city’s total area.

Development outside of the serviced area is serviced by subsurface disposal systems representing less than 5 percent of the city’s population.

At present (1995), the sewer serviced area of the City of Nashua is divided as follows:

The City of Nashua presently (May 16, 2007) has 22,653 active residential and commercial Residential Wastewater Service Permits and Drain Permits dating from 1892.

The City of Nashua also services the majority of Hudson, NH, and receives and treats a small amount of sewerage from Merrimack, NH