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2015 Census of Public Water Systems


Each year the Missouri Department of Natural Resources publishes the Census of Missouri Public Water Systems. I reported on the 2013 census here, and the 2014 census here. This post updates the information for 2015.

Public Water Census 2015The census provides basic information about the number and type of public water systems in the state, plus information on each system that includes the source of its water, the type of treatment it gives the water, and a chemical analysis of the water that covers 16 inorganic chemicals. The table at right shows the summary data for 2013-2015.

A primary water system is one that obtains water from a well, infiltration gallery, lake, reservoir, river, spring, or stream. A secondary water system is one that obtains its water from an approved water system, and distributes it to consumers. (Missouri 10 CSR 60-2015, Definitions) About 78% of Missouri public water systems are primary systems, and they serve about 77% of the population.

The EPA defines a public water system as one that provides water for human consumption to at least 15 service connections or that serves an average of at least 25 people for at least 60 days a year. It classifies public water systems in three categories. Community Water Systems (CWS) supply water to the same population year-round. Non-Transient Non-Community Water Systems (NTNCWS) supplies water to at least 25 of the same people at least 6 months per year, but not year-round. An example might be a school that has its own water system. A Transient Non-Community Water System (TNCWS) provides water in a place where people do not remain for long periods of time. Examples might include gas stations or campgrounds that have their own water systems.

There were 2,722 public water systems in Missouri. The number of community systems in Missouri increased by one in 2014, then decreased by 14 in 2015. NTNCWS systems decreased by 3 in 2014, then increased by 5 in 2015. TNCWS systems decreased by 20 in 2014, then increased by 15 in 2015.

Groundwater means groundwater that is not directly influenced by the surface water above it. The groundwater is isolated from surface groundwater by thick layers of rock or sediment that filter the ground water before it reaches the groundwater aquifer. Groundwater Under Direct Influence refers to groundwater that is not protected from the surface water above it, and which consequently contains groundwater contaminants, such as insects, microorganisms, algae, or turbidity. This kind of water and surface water, require more extensive treatment before they are fit for use.

In 2015 there were 217 surface water systems (about 15% of all systems), but they served a population of 3,534,956 (about 64% of Missouri’s population). There were 1,210 groundwater systems (about 84% of all systems), and they served 1,980,271 (about 36% of the population). Between 2014 and 2015 the number of surface water systems increased by one, and they served 174,734 more people. The number of groundwater systems decreased by 15, and they served 2,607 more people.

Most of the water systems in Missouri source their water from groundwater, only a few from ground water under direct influence. However, the source serving the largest population is surface water. Specifically, the Missouri River is the water source for much of the Kansas City and St. Louis metropolitan areas. More than half of Missouri’s population is served by water either from the Missouri River Alluvial Aquifer or water from the river itself.


Missouri Department of Natural Resources. 2015. Census of Missouri Public Water Systems, 2015. http://dnr.mo.gov/pubs. This URL will take you to a long list of publications available from MoDNR. Scroll down to Public Drinking Water to find the census reports.

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