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National Contaminant
Occurrence Database (NCOD)
EPA developed the NCOD to satisfy the
statutory requirements set by Congress in the 1996 amendments to the Safe
Drinking Water Act (SDWA) to maintain a national drinking water contaminant
occurrence database using samples data for both regulated and unregulated
contaminants in public water systems.
This site provides a listing of water sample analytical data that EPA is currently using and has used in the past for analysis,
rulemaking, and rule evaluation.
The data have been extensively checked for data quality and analyzed for
national representative-ness.
From this site you can access the Microsoft Excel PivotTables® of the various samples data to help
you access, organize, and analyze the data by contaminant, geography,
sample date, and various water system attributes. You can also download
the underlying databases.
You can access both the latest UCMR data,
which are being collected and added to the NCOD, as well as static datasets
that have been used in published regulatory analyses. These latter (static)
datasets have been extensively quality-checked, and their corresponding
reports provide full descriptions (meta data) of the data. You can
also analyze the data across several attributes using the PivotTables. Brief
descriptions of the NCOD data sets and their corresponding links are included below.
Unregulated Occurrence Data
Unregulated occurrence data are sample data from monitoring in public
water systems for contaminants not having health-based standards set under
the SDWA at the time of the monitoring.
- Historical (Rounds 1 & 2)
The Round 1 dataset contains public water system monitoring sample results for 62 (then) unregulated contaminants, generally collected between 1988 and 1992, from 40 states and primacy entities. The Round 2 dataset (the second round of unregulated contaminant monitoring)
contains public water system monitoring sample data for 48 (then) unregulated
contaminants, generally collected between 1993 and 1997, from 35 states
and primacy entities.
- Unregulated Contaminant Monitoring Rule 1 Data
The occurrence data associated with the revised UCMR (1999) is meant to assist the Agency in determining whether or not to regulate a certain contaminant. The UCMR (1999) was designed to assess contaminant occurrence nationally. Therefore, extreme caution should be used in any interpretation of data, which reflects only a subset of the entire database. The monitoring is scheduled during the period from 2001 until 2003
SixYear Review of National Drinking Water Regulations
The SDWA requires EPA to review each national primary drinking water regulation (NPDWR) at least once every six years and revise them, if appropriate. SDWA specifies that any revision must maintain or increase public health protection. EPA conducted detailed contaminant occurrence analyses for 61 regulated contaminants, using data provided by a national cross-section of 16 states. Most of the sample data were collected between 1993 and 1997
Ambient/source water data
EPA maintains two data management systems containing water quality information for the nation's ambient waters, the Legacy Data Center and STORET. Both systems contain raw biological, chemical, and physical data on surface and ground water collected by federal, state and local agencies, Indian Tribes, volunteer groups, academics, and others. All 50 States, territories, and jurisdictions of the U.S., along with portions of Canada and Mexico, are represented in these data systems.
- Legacy Data Center
The Legacy Data Center, or LDC, contains historical water quality data dating back to the early part of the 20th century and collected up to the end of 1998.
- STORET
The STORET database contains data collected beginning in 1999, along with older data that has been properly documented and moved from the LDC.
U.S. Geological Survey (USGS)
The USGS disseminates water data it has collected to the public through a system called the National Water Information System (NWIS). Many types of data are stored in the NWIS network, including: site information, time-series (flow, stage, precipitation, chemical), peak flow, and groundwater and surface water quality measures.
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