Water Infrastructure Management
Given Philadelphia's history as one of America's earliest-developed cities, the age, physical condition, and efficiency of its infrastructure requires continuous inspection and maintenance. This section will explain the issues the Water Department must address.
Traditional Infrastructure Basics
Philadelphia has an extensive history in water management practices that dates back more than 200 years and comes with the need to monitor the physical condition of this aging infrastructure network. The City’s water and wastewater systems have the distinction of being one of the first in the country. When the Fairmount Water Works began operating in 1815, approximately 63 homes were connected by wooden mains to its reservoir, which was located on the hilltop now occupied by the Philadelphia Museum of Art.
The Water Department's primary mission is to plan for, operate, and maintain both the infrastructure and the organization necessary to supply high quality drinking water, to provide an adequate and reliable water supply for all household, commercial, and community needs, and to sustain and enhance the region's watersheds and quality of life by managing wastewater and stormwater effectively.
Maintenance of the existing infrastructure is one of the most important aspects of the work performed by the Philadelphia Water Department (PWD). Maintaining the City’s water supply and distribution system ensures that PWD is able to distribute enough clean, drinkable to all its users. Preserving Philadelphia’s existing wastewater and stormwater systems prevents tons of pollution from entering the waterways. In order to sustain the existing infrastructure, the Water Department employs several different tools and programs to uphold the Water Department’s commitment.
To better understand how our systems work, it is important to understand how an urban water cycle operates which is a modified version of a natural water cycle. Click here to observe a diagram of how the water cycle might work in Philadelphia.
What makes up our infrastructure system?
PWD has approximately 3,000 miles of sewers, 79,000 stormwater inlets, three drinking water treatment plants, three wastewater treatment plants, more than 25 pump stations, 175 CSO regulating chambers, 164 CSO outfalls, more than 3,000 miles of water mains, 18 reservoirs, five water storage tanks, and more than 450 stormwater outfalls.
Philadelphia’s water supply and distribution system serves approximately a 130-square-mile area. The drinking water treatment plants draw water from the Schuylkill and Delaware rivers and process the river water through various testing and treatment stages to make the water safe and drinkable. The Water Department then distributes the water to approximately 1.5 million Philadelphia residents through more than 3,000 miles of water mains.
These mains range in size from 6 to 93 inches in diameter. Eighty-seven percent of Philadelphia's water mains are cast iron, the water industry's material of choice until the mid-1960s. At that time, the introduction of ductile iron pipes revolutionized the industry because this material is stronger and more flexible than cast iron. In addition to the water mains, there are about 83,800 line valves and approximately 27,700 standard pressure fire hydrants.
The Water Department operates three drinking water treatment plants: Baxter, Belmont, and Queen Lane, located in close proximity to the Schuylkill and Delaware Rivers. The plants distribute enough water to supply not only all of Philadelphia’s residents and businesses but also provide some drinking water to other counties.
The Philadelphia wastewater and stormwater conveyance system is divided into three drainage districts: Northeast, Southeast, and Southwest. Through a network of various components, each district conveys flow to its respective Wastewater Treatment Plant (also referred to as Water Pollution Control Plant, or WPCP) of the same name.
The wastewater system is composed of brick, concrete and vitrified clay piping which are egg-shaped, circular or rectangular and range from 8 inches to 22 feet in diameter. The system is roughly 50% brick, 25% vitrified clay and 25% reinforced concrete pipe.
The infrastructure components of our wastewater and stormwater conveyance system include branch sewers, trunk sewers, combined sewer interceptors, separate sanitary interceptors, and storm relief sewers. Branch sewers collect wastewater from lateral connections (connections from houses and businesses) and the wastewater is transported through a series of increasingly larger pipes to a regulating chamber. The regulating chamber then regulates how much wastewater flow goes to the treatment plant. Combined sewer interceptors convey flow from regulating chambers and separate sanitary interceptors to the WPCPs. Storm relief sewers convey flow from storm relief diversion chambers to the receiving waters during extreme high flow.
How long is the infrastructure expected to last?
This is a difficult question to answer, since the age of our infrastructure (such as brick sewers) is not necessarily the indicator of potential failure. Pipes can break due to many factors such as nearby disturbance or pressure changes, etc. Over the years, many different types of material have been used in our infrastructure. For instance, cast iron was used in water mains prior to 1967 while ductile iron is now used. Also, a pipe that carries water is not built the same as a pipe that is built to carry wastewater; therefore its lifespan is not necessarily the same. And all cast iron pipes develop some issues if they are not cleaned and/or cement-lined throughout their lifetime. So infrastructure longevity can depend on various factors including pipe type, construction technique, location, maintenance history, and age. Necessary infrastructure maintenance is well evaluated using an extensive point system - which ranks the pipes for replacement based on fractures per mile/block, age, and other factors – for the water lines and the Sewer Assessment Program is used to survey the wastewater lines. PWD’s water and wastewater replacement rates are roughly 100 to 120 years, replacing about 20 miles of water main and 8 miles of sewer pipe each year. More miles of water lines are replaced than wastewater because wastewater maintenance costs about twice the amount of water infrastructure maintenance due to the deeper excavation and materials.
How old is our infrastructure (pipes, plants, etc)?
The average age of one of our water lines is roughly 78 years old, with some pipes dating back to 1824. The average age of the wastewater lines is about 100 years. The map on the left shows that the installation date of the original wastewater pipes varies depending on the section of the City; this would be somewhat similar for the water and stormwater pipes. In general, areas around central Philadelphia (North Philadelphia, Center City, Old City and parts of South Philadelphia) have the oldest original installation dates at over 150-200 years. As the City began to grow out toward the far Northeast, Northwest, and Lower South Philadelphia, infrastructure was built to accommodate the needs of the people and businesses residing in these new locations.
The drinking water treatment plants are roughly about 100 years old, but they are constantly being upgraded.
The wastewater treatment plants are newer, between 60-87 years old. These plants are frequently being rebuilt and renovated to meet stricter federal water pollution control laws.
How does its age compromise its efficiency?
Again, age may not compromise efficiency unless it is extreme. Age may suggest the potential for an efficiency issue, but it is not a stand-alone factor that PWD depends on. Again, material type, construction technique, location, break type, maintenance history, age and other factors dictate the service life of the infrastructure. PWD's asset management program suggests the Water Department’s operation management is comparable to other cities in the U.S. and internationally. The Water Department participated in the International Water Association (IWA) and the Water Services Association of Australia (WSAA) study for Asset management where PWD was considered a practice leader for some of our approaches.
What other issues is the Water Department concerned about?
Our goal is not only to maintain the city's water quality but also to improve the condition of our environment. Controlling pollution is a primary concern, therefore efforts to lower the amount of pollutants released into our watersheds are always being evaluated. Of the more than 3,000 miles of sewers that collect wastewater and stormwater (sometimes in the same pipe), the pipes PWD has the least amount of control of are the ones that carry flow from homes to street sewers. These small sewers are referred to as laterals. These laterals are normally five to six inches in diameter. Being so small and numerous, laterals are sometimes susceptible to breaks and improper installation, which can release wastewater into our waterways.
It is important to note that the Office of Watersheds does not normally conduct a lot of work in the water supply and distribution system. It does conduct research and planning to protect the waterways and watersheds, which benefits the water supply that is distributed. For more information on the water distribution system, please visit the Water Department's Website