Domestic Wells in the United States
Where are domestic wells located and how many people use them?
Domestic wells provide drinking water supply for approximately 40 million people in the United States. Knowing the location of these wells, and the populations they serve, is important for identifying heavily used aquifers, locations susceptible to contamination, and populations potentially impacted by poor-quality groundwater.
USGS personnel sampling a well for nitrates. Nitrate is one of many constituents the USGS analyzes in order to assess the quality of the drinking-water aquifer. Photo by Stefan Voss, USGS.
In a recently published article (Johnson et al 2019), the authors found there is a relationship between the proportion of people using domestic wells (Domestic Ratio (DR)) and the household density (HD, as households per square kilometer).
- As household density increases, the ratio of people using domestic wells goes down, after an initial threshold is reached. This relationship can be expressed in the diagram below.
Conceptual illustration of the relationship between the proportion of people using domestic wells (Domestic Ratio, DR) and the household density (HD). Units for HD are households per square kilometer.
"The relationship we saw in the data fits with our anecdotal observations: there are relatively few domestic wells in cities because most people are connected to municipal supply. In contrast, sparsely inhabited rural areas have a high ratio of people using domestic wells because city water is not available." Tyler Johnson, Research Geographer, USGS
After constructing the relationship, the authors were able to create several maps showing the number of people being served by domestic wells. One of the maps (shown below) uses the fundamental assumption that domestic wells are located near a home.
This map shows the number of people using domestic wells per square kilometer for the year 2010.
The map is based on the "Road-Enhanced Method" which locates domestic wells near roadways ( Johnson and Belitz 2017 ).
The assumption is that domestic wells are usually located near a home and homes are usually near a named roadway.
Densely populated cities have a lower percentage of people using domestic wells than do rural areas.
The population using domestic wells varies by state. Michigan has the most domestic well users at nearly 2.5 million people.
The percentage of people using domestic wells tells a different story. Michigan may have the most domestic well users, but Maine has the highest percentage of users. Over 38% of the population of Maine uses a domestic well.
The Southwest states of Arizona, California, Nevada, and Utah have the lowest percentage of domestic well users. However, their total number of users is over 1.5 million people combined.
The percentage of people using domestic wells has been decreasing nationally. However, some states have increased their usage (as DR) over time.
There may be several reasons for this trend including that population is increasing in urban areas with access to city water faster than in rural areas without access. Household size is also falling, therefore a single well will serve fewer people.
For more information, the full report can be found online:
Johnson, T.D., Belitz, K., Lombard, M.A., 2019, Domestic well locations and populations served in the contiguous U.S. for 2000 and 2010: Science of the Total Environment, v. 687, p. 1261-1273. https://doi.org/10.1016/j.scitotenv.2019.06.036 .
The data sets can be found and downloaded here:
Previous work describing the Road Enhanced Method:
Johnson, T.D., Belitz, K., 2017, Domestic well locations and populations served in the contiguous U.S.: 1990, Science of the Total Environment 607-608C, pp. 658-668, https://doi.org/10.1016/j.scitotenv.2017.07.018 .
Additional information about the USGS National Water Quality Program (NAWQA) can be found here:
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