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Plumbing, explained

Longer reads for owners, boards and property managers who want to understand a system before deciding on repairs.

§ 01

Data: lead service lines in NYC

NYC residential water service lines by material statusData
Bar chart; values are listed in the table view below. 0125,000250,000375,000500,000 Potential lead: 136,891 service-line records Potential lead 136,891Unknown material: 227,443 service-line records Unknown material 227,443Not lead: 490,338 service-line records Not lead 490,338

What it shows: Of 854,672 records, 16.0% were classed potential lead and 26.6% unknown. In June 2024, DEP testified to at least 130,000 known lead lines (an estimated ~150,000) and about 200,000 of unknown material, which is consistent with this picture. DEP publishes a building-by-building map.

Units
Service-line records (count)
Geography
New York City, residential properties
Data period
Records analyzed in 2022
Source
medRxiv preprint 2022.10.11.22280958 (analysis of DEP records); cross-checked with DEP testimony, June 2024
Last updated
November 4, 2026

"Not lead" is computed as total records minus the two other categories. Preprint figures are not peer-reviewed; use DEP's current map for any individual property.

Table view
NYC residential water service lines by material status
StatusRecords
Potential lead136,891
Unknown material227,443
Not lead490,338
§ 02

Diagram library

Typical gas tank water heater connectionsDiagram D5
  • Cold water
  • Hot water
Typical gas tank water heater connections A tank water heater with a cold-water inlet and shutoff valve, a thermal expansion tank on the cold side where required, a hot-water outlet, a temperature and pressure relief valve with a discharge pipe ending near the floor, a drain valve at the bottom, and a gas supply with a shutoff valve and sediment trap. The flue vent rises from the top. Requirements vary by code and model. flue vent expansion tank T&P relief valvedischarge pipe ends near floor drain valve gas supply + shutoffsediment trap 123456
  1. 1Cold-water inlet with shutoff valve
  2. 2Thermal expansion tank (where required, e.g. with a check valve or pressure regulator)
  3. 3Hot-water outlet to fixtures
  4. 4Temperature & pressure (T&P) relief valve and discharge pipe: never cap or plug it
  5. 5Drain valve for flushing sediment
  6. 6Gas supply with shutoff and sediment trap: gas work is for licensed professionals only

Simplified. Requirements vary by code, jurisdiction and manufacturer. Gas work must be done by licensed professionals.

Apartment building riser with roof tankDiagram D2
  • Cold water
  • Hot water
  • Drain / waste / sewer
  • Vent
Schematic of water supply and drainage in a ten-story New York apartment building City water enters the basement. A house pump lifts water through an up-feed pipe to a roof tank. Gravity then feeds a down-feed riser that branches to each floor, so pressure is lowest on the top floors closest to the tank. In some buildings, lower floors are fed directly by street pressure. A drain stack collects waste from every floor and runs down to the building sewer, with a vent through the roof. Configurations vary; some buildings use booster pumps instead of a tank. STREET 10987654321 BASEMENT roof tank house pump lowerpressure higherpressure 12345678
  1. 1City water enters at street pressure. In NYC that is typically enough to reach about six stories
  2. 2House pump lifts water from the basement
  3. 3Up-feed line to the roof tank
  4. 4Roof tank stores water; gravity creates the pressure below