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Water: Public Water Systems

Public Drinking Water Systems: Facts and Figures

For more detailed statistics on public drinking water systems and violations of drinking water rules, read Factoids: Drinking Water & Ground Water Statistics or investigate getting access to drinking water data.

There are approximately 155,000 public water systems in the United States.  EPA classifies these water systems according to the number of people they serve, the source of their water, and whether they serve the same customers year-round or on an occasional basis.  The following statistics are based on information in the Safe Drinking Water Information System (SDWIS), for the fiscal year ended September 2008, as reported to EPA by the states. 

Classifications:

Public water systems provide water for human consumption through pipes or other constructed conveyances to at least 15 service connections or serves an average of at least 25 people for at least 60 days a year. EPA has defined three types of public water systems:

  • Community Water System (CWS): A public water system that supplies water to the same population year-round.

  • Non-Transient Non-Community Water System (NTNCWS): A public water system that regularly supplies water to at least 25 of the same people at least six months per year, but not year-round. Some examples are schools, factories, office buildings, and hospitals which have their own water systems.

  • Transient Non-Community Water System (TNCWS): A public water system that provides water in a place such as a gas station or campground where people do not remain for long periods of time.
EPA also classifies water systems according to the number of people they serve:

  • Very Small water systems serve 25-500 people
  • Small water systems serve 501-3,300 people
  • Medium water systems serve 3,301-10,000 people
  • Large water systems serve 10,001-100,000 people
  • Very Large water systems serve 100,001+ people

Number of Systems and Population Served for 2010:

(note:  populations are not summed because some people are served by multiple systems and counted more than once)

  • 52,873 CWS served 300.2 million people
  • 19,400 NTNCWS served 6.4 million people
  • 87,672 TNCWS served 13.1 million people
Number of Systems and Population Served

Source Water System Size
Community Water System (CWS)
  • 11,976 systems relied on surface water, serving 210.7 million people


  • 40,813 systems relied on ground water, serving 89.4 million people
  • 23% of CWS are very large, large, or medium, serving 70% of those who get their water from a CWS


  • 77% of CWS are small or very small, serving 30% of those who get their water from a CWS
Non-Transient Non-Community Water System (NTNCWS)
  • 776 systems relied on surface water, serving 869,312 people


  • 18,581 systems relied on ground water, serving 5.5 million people
  • 96% of NTNCWS are small or very small, serving 86% of those served by NTNCWS


  • 4% of NTNCWS are medium, large, or very large, serving 14% of those served by NTNCWS
Transient Non-Community Water System (TNCWS)
  • 2,190 systems relied on surface water, serving 2,575,140 people


  • 85,303 systems relied on ground water, serving 10.5 million people
  • 97% TNCWS are small or very small, serving 80% of those served by TNCWS


  • 3% of TNCWS are medium, large, or very large, serving 20% of those served by TNCWS
More on Public Drinking Water Systems

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