Navigating these web pages...

The USGS Groundwater Watch pages present groundwater level data from wells currently in a regular measurement program.

Individual wells can be present in multiple networks.  For instance, a well with real time instrumentation that is designed to monitor climate effects will be present in at least 3 networks:  Real Time, Climate Response, and Active Water Levels.

Because most USGS wells are supported through State and local agencies, these web pages generally are designed using political boundaries: by State.  If the network contains a large number of wells, there also is a county “layer” of pages. Networks organized by U.S. Principal Aquifers are organized by state and county within the individual Principal Aquifer.

A user has several options for viewing the color-coded maps of water level "conditions", which are the tool for drilling down to individual wells.

(1) Static maps created by the MapPoint^® software:  These image files are relatively small, providing fast navigation even with slow internet connections. 

(2) Interactive maps created using Google Maps:  These maps provide the user with more flexibility such as the ability to zoom and pan, and to view different backgrounds, such as roads, satellite photography, or USGS topographic maps.  One limitation to this approach is the speed at which the pages are “rendered”, or drawn by the browser.  The rendering speed is affected by the number of wells in the map.  Thus the maps from states or counties with many wells can take a long time to render.  We have compromised some flexibility for rendering speed by limiting the number of wells we present in individual maps.  County maps contain all of the wells in the county, and additional wells (depicted with low color intensity) in a small buffer around the county boundary.  State maps contain all the wells in the State, and additional wells (depicted with low color intensity) in a small buffer around the State boundary. 

(3) Interactive maps using Google Earth:  Google Earth .kmz files are created daily for each network, and available on the National Map (containing all wells in the network), or on the State map (containing only wells in that State).  Use of .kmz files requires the user to install Google Earth software on their local computer.  Google Earth software is available at no cost at http://earth.google.com/ . Users are reminded that the color-coded networks map .kmz files must be downloaded each day for an up-to-date view of the network.  Individual wells within a Google Earth view should always be up-to-date regardless of when the .kmz files were obtained.

Explanation for Types of Data

There are three types of water-level data available from wells measured by the USGS:

(1) Periodic data are groundwater levels that are incrementally measured, by hand at selected intervals, usually with a steel or electric tape. These measurements typically are made monthly to quarterly. Thus periodic data displayed in on these web pages may be the most recent measurement from the well, but still several months old. Periodic data are considered to be approved data once they are presented on the internet. A triangle is used to symbolize a well with periodic data in Groundwater Watch.

(2) Continuous data are groundwater levels measured by an automatic sensing device, recorded by a data logger, and periodically retrieved from the well. The availability of continuous data may lag current conditions by one to several months because they must be retrieved from the field, processed, and loaded into the USGS database. Some continuous data are provisional and subject to revision. A square is used to symbolize a well with continuous data in Groundwater Watch.


(3) Real-time data are continuous data that are transmitted from the well to the USGS by usually satellite or telephone at least once per day. Real-time data reflect current groundwater conditions in the well. The real-time data presented on these web pages are one day behind because of the statistical calculations used in the data presentation. All real-time data are provisional and subject to revision. A circle is used to symbolize a well with real-time data in Groundwater Watch.

Data Updates

Each weekend, all Groundwater Watch networks are refreshed and old contents are completely replaced with new. Therefore, new wells added to NWISWeb during the week will not show up on Groundwater Watch until Monday morning.

Each weekday, data are updated for sites already in Groundwater Watch, beginning at 4:30am,  starting  with states on the east coast and progressing to the west by time zone. Therefore, maps and data for the nation are not completely up-to-date until after 1pm each day.

Provisional Data Disclaimer

Data from real-time groundwater wells, and wells with continuous instrumentation that are not transmitted in real time are considered to be Provisional Data because they have not yet been reviewed and finalized, or approved, by the USGS. These data may be subject to significant revision and should not be cited until reviewed and approved by the U.S. Geological Survey. Data users are cautioned to consider carefully the provisional nature of the information before using it for decisions that concern personal or public safety or the conduct of business that involves substantial monetary or operational consequences.

Provisional Groundwater Data are incrementally approved over the course of a year. On these web pages, the approval status of an individual measurement can be determined by (a) the color of the measurement as presented in a hydrograph (red=provisional; blue=approved), and/or the “status code” that is attached to each measurement in the “download data” option.

Explanation of a Percentile

Water-level measurements are presented within a statistical framework.  The percentile provides this statistical framework.  A percentile is a value on a scale of one hundred that indicates the percent of a distribution that is equal to or below it. For example, on the map of groundwater levels, the water-level at the 90th percentile is equal to or greater than 90 percent of the monthly mean groundwater levels in a given month over the period of record at the well. In general,

·  a percentile greater than 90 is considered much above normal

·  a percentile greater than 75 and less than 90 is considered above normal

·  a percentile between 25 and 75 is considered normal

·  a percentile less than 10 and less than 25 is considered below normal

·  a percentile less than 10 is considered much below normal

The water-level category “New Low” indicates that the most recent groundwater level measurement is lower than the lowest monthly mean groundwater level in the month of measurement over the period of time that the well has been measured. Similarly, the water-level category “New High” indicates that the most recent groundwater level measurement is higher than the highest monthly mean groundwater level in the month of measurement over the period of time that the well has been measured.

The water-level category “Not Ranked” indicates that a water-level category has not been computed. This is most often due to the fact that there have not been at least 10 years of water-level measurements in the month of the most recent measurement. In the Climate Response Network, a measurement also will be categorized as “Not Ranked” if the measurement is more than 45 days old.

Explanation for Groundwater Level Statistics on these pages

The frequency of groundwater measurements is determined by technical and economic factors. Technically, the frequency of measurement is based on the expected variability of the water-level fluctuations and the objectives of the measurements. A shallow well used to monitor drought conditions may be measured hourly and have real-time instrumentation. A deep well in a confined aquifer with a stable water level, or stable water-level trend may be measured once per year. For economic reasons, the measurement frequency at a well may change over time from continuous to periodic due to fluctuations in available funds.

The statistical approach presented in these web pages reflects the diversity of the data sets available for individual wells across the United States. Ideally and for statistical simplicity, hourly or daily values would be available for 30 or more years from every well in every network. However, that is not the case, nor is it even appropriate in some cases to adequately characterize the water level in an aquifer.

In these pages, water-level measurements are evaluated within a monthly statistical framework. This process allows us to take a uniform approach for wells with frequent data collection and wells with infrequent data collection.

Four different statistical summaries may be available for a given well. An explanation for these for summaries is included below.


All available data (periodic and continuous) from an individual well are combined and a median for each Month/Year combination is created. These Month/Year medians are then grouped by month, and the median of the grouped data is used to represent the value for a given month in a given year. Provisional data that have not received final USGS approval are not included in these statistical calculations.

These monthly means are then ranked, and the appropriate statistics are presented based on the following criteria. If there are 4 or less years of data for any given month, no statistics are computed for that month. If there are more than 4 years and less than 10 years of data in a given month, the minimum, median, and maximum water levels are displayed in the table, and plotted in the adjacent hydrograph using a vertical line. If there are 10 or more years of data in a given month, water-level percentiles are computed and displayed in a table and in the adjacent hydrograph using colored monthly bars.


This section of the web page presents basic statistics using only the continuous record available from a well. The entire population of daily values from a well is ranked (regardless of day or month). Percentiles then are computed based on the entire population of daily values. The daily value used in this calculation is determined by the individual USGS office responsible for the data collection, and may be the daily minimum, daily mean, daily maximum, or noon measurement for the day. When multiple types of daily values are available (min, mean, max), the daily value with the longest period of record is used. Provisional data that have not received final USGS approval are not included in these statistical calculations.


This section of the web page presents basic statistics using only the periodic record available from a well. The entire population of periodic measurements from a well is evaluated, and the highest and lowest periodic measurements are presented. Periodic measurements available on the web are approved data, and all data are used in statistical calculations.


This section of the web page presents basic statistics using all of the available measurements available from a well, and does not restrict it to approved data. The periodic measurements and daily values described above are combined with provisional continuous and real time data. The entire population is evaluated, and the highest and lowest values are presented.

Summary of Networks available on Groundwater Watch

National Networks

Active Groundwater Level Network

The Active Groundwater Level Network contains water levels and well information from more than 20,000 wells that have been measured by the USGS or USGS cooperators at least once within the past 365 days. This network includes all of these wells, regardless of measurement frequency, aquifer monitored, or the monitoring objective.

Climate Response Network

The USGS maintains a network of wells to monitor the effects of droughts and other climate variability on groundwater levels. The network consists of a national network of about 140 wells monitored as part of the Groundwater Resources Program, supplemented by wells in some States monitored as part of the Cooperative Water Program.

Real-Time Network

Real-time data typically are recorded at 15-60 minute intervals, stored onsite, and then transmitted to USGS offices every 1 to 4 hours, depending on the data relay technique used. Recording and transmission times may be more frequent during critical events. Data from real-time sites are relayed to USGS offices via satellite, telephone, and/or radio and are available for viewing within minutes of arrival.

Long-Term Groundwater Data Network

The Long-Term Groundwater Data Network is comprised of active wells measured on a periodic, monthly or yearly basis for periods of 20, 30 or 50 years, whose records are at least 80% complete.

The following measurement frequencies are selectable in these pages

Annual Data:	at least 1 measurement per year (includes monthly and daily wells)
Monthly Data:	at least 1 measurement per month (includes daily wells)
Daily Data:	at least 1 measurement per day.

The user can select from the following lengths of record:

20 years: 20 or more years of record (includes data in 30 and 50 year data set)

30 years: 30 or more years of record (includes data in 50 year data set)

50 years: 50 or more years of record.

To be included in the data set, the well record must be 80% complete over the period of interest. For example, selecting wells with 30 years of monthly data means that all wells in the data set will have at least 288 months of measurements (30 yrs x 12 months x 80%).

By selecting among the various frequency and length of record radio buttons, a user can select the datasets of interest, organized by state.

Regional Networks

High Plains Regional Groundwater Level Monitoring Network

The High Plains Regional Groundwater Level Monitoring Network contains water levels and well information from selected wells measured annually by the USGS and numerous Federal, State, and local water-resources agencies. A network of about 9,000 wells was used to monitor water levels in the High Plains aquifer in 2007. This network consists of many smaller networks of wells measured by numerous agencies. State and local agencies are responsible for the majority of the water-level measurements. The water-level measurements were collected in winter or early spring when irrigation wells typically were not pumping and water levels generally had recovered from the stress of pumping during the previous irrigation season.

State and Local Networks

Work on state and local networks is in progress.