Private Inflow & Infiltration (I&I)

Private Inflow & Infiltration (I&I)

 What is a private inflow?

 Inflow is rainwater that enters into the sanitary sewer through private connections (i.e. roof drains and leaders, sump pumps, driveway drains, uncapped cleanouts, foundation drains, floor or yard drains) to the sewer system.

These sources are improperly or illegally connected to the sanitary sewer system via either direct connections or discharge into sinks or tubs that are directly connected to the sanitary sewer system.


What is a private infiltration?

Infiltration is groundwater or rainwater that enters into the sanitary sewer through sewer service laterals that have leaking or separated joints/connections or through damaged/broken pipe (i.e. cracks, holes).

 Infiltration often exhibits seasonal variation in response to groundwater levels.  Storm events can trigger a rise in groundwater levels and increase infiltration flows.  The highest infiltration flows are observed following significant storm events or following prolonged periods of precipitation.

Private Inflow/Infiltration Illustration

Several examples of Inflow and Infiltration that may exist on private property and how these sources are connected to the public sanitary sewer.




Why private inflow and infiltration matters?

Inflow and infiltration water is referred to as “clear water”, distinguishing it from sanitary sewage water.  When “clear water” gets mixed into the sanitary sewer system it takes up valuable capacity within the collection system and at the wastewater treatment plant.

Excess inflow and infiltration can cause Sanitary Sewer Overflows (SSOs) that violate the Clean Water Act. SSOs occur when the sanitary sewer capacity is exceeded and sewage comes out of manholes or results in sewer back-ups into homes and businesses. SSOs can have a detrimental effect on the ecology of the Long Island Sound, reduce water quality for recreation, and create unhealthy environmental conditions for City residents.


Who is responsible?

Property owners are responsible for the repair and maintenance of their sewer laterals from the building to the connection at the sanity sewer main.

Inflow type connections to the sanitary sewer are illegal as dictated by the City Code.


How to locate inflow and infiltration sources?

There are several ways for plumbers to locate private inflow or infiltration sources with the use of closed circuit television (CCTV) inspection, dye testing, and smoke testing.


  • CCTV Inspection: A robotic camera system that is sent down a sanitary sewer line to inspect and record the pipe conditions.  CCTV inspections can identify breaks, root intrusions, leaking water and other deteriorating conditions.


A diagram showing the CCTV camera system set up where the robotic camera can detect damages that can be found in a pipe.


  • Dye Testing: By pouring non-toxic fluorescent colored dye down roof drains, driveway drains, pump sumps, and other potential sources will provide verification if the drain being tested is directly connected to the sanitary sewer.


dye test

Dye testing example that shows the florescent dye used to indicate a source of inflow and infiltration in a sewer system.


  • Smoke Testing: This involves pumping non-toxic smoke into City-owned sanitary sewer manholes and observing where the smoke exits.  The exiting smoke can indicate a broken pipe or identify where roof or foundation drains are improperly connected to the sanitary sewer system.

smoke test

Smoke escaping from a roof drain (left) and a floor drain (right) during an inflow and infiltration smoke test.


How to fix inflow and infiltration problems?

 If you have a confirmed illegal connection, you must modify the plumbing on your property to redirect your inflow source to the appropriate location. Please note your new chosen drainage location should not create a nuisance condition for your neighbors or in a public right of way. Please consider this when developing your discharge strategy.

Replace any known broken, leaky, or problem sections of your property’s sewer lateral.  Clay tile sewer laterals are subject to cracks and offset joints.  Orangeburg sewer laterals are composed of layers of wood pulp and pitch pressed together are brittle and subject to collapse.

Examples of cleaning, replacing or rehabilitating broken sewer laterals include hydro jet lateral cleaning, lateral replacement (excavation), and Cured In Place Pipe (CIPP) lining.


  • Hydro Jet Lateral Cleaning: A blast of water at a high pressure is sent through lines that will usually remove most blockages and build up.


jet cleaning

An example of Hydro Jet Lateral Cleaning


  • Lateral replacement (excavation): Involves trenching to find and replace sewer lateral.



  • CIPP Lining: Involves trenchless pipe repair by pulling a resin-saturated liner through a damaged pipe, which is then cured with steam or hot water to form a tight fitting, joint less replacement pipe.



Cured in place pipe repair example (before and after)


Customer Service Center:

If you have questions, or would like additional information on private I&I removal, please contact our Customer Service Center at 203-854-3200.

  • Customer Service Center – Help Desk (Link:


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