Ground water is a critical natural 

resource used as a source of drinking 

water by more than 140 million people 

nationwide. Measurements of groundwater levels from wells are used to observe 

the effects of hydrologic stresses on an 

aquifer. These data are needed to monitor 

responses to climate and to ground-water 

development. Ground-water-level data are 

used to quantify aquifer recharge, as a calibration tool for ground-water models, and 

to support water-quality investigations.

Ground-water levels can be measured 

“continuously” or periodically. Periodic 

water-level measurements are those made 

manually at scheduled intervals, usually 

with a steel or electric tape. Continuous 

ground-water-level data are measured by 

an automatic sensing device, recorded by 

data loggers, and retrieved periodically 

from the field. The availability of these 

data lags current conditions by one to several months. During drought, when these 

data are in high demand, most areas of 

the Nation do not have timely data needed 

for effective ground-water management 

decisions. The technology now exists for 

continuous collection, transmittal, and processing of ground-water-level data to a 

central location for display of real-time 

ground-water conditions over the Internet 

when the data are needed most.

Real-time ground-water data are 

defined herein as data automatically collected, transmitted, and made available to 

the public at least once per day. These data 

can be transmitted by land-line telephone, 

cellular telephone, land-based radio frequency (RF) technology, satellite telemetry, or a combination of these technologies. 

Satellite telemetry is the most common 

method used for real-time data transmission within the U.S. Geological Survey. 

Although some water-quality characteristics can be continuously monitored in 

wells, water levels are the most common 

data transmitted in real time by the USGS.

3. Data Availability—Real-time information promotes interest in ground-water 

data by bringing ground water to the 

public eye. Today more than ever, data 

users expect information to be available 

when and where they need it. With the 

USGS online National Water Information 

System (NWISWeb), ground-water levels 

can be served to the public almost immediately upon entry into the database. As 

timely, reliable data become the norm, 

more and more organizations and individuals will use the data, perhaps in unexpected ways.

4. Cost—The cost benefit of real-time 

data collection often is debated. Equipment and installation costs for real-time 

instrumentation are higher than for traditional methods. However, data-processing 

time and site visits can be significantly 

reduced. Real-time instrumentation is particularly beneficial at sites where access 

is difficult due to landowner restrictions 

or the remote nature of the site. One of 

the most overlooked aspects of real-time 

data is the decreased equipment costs and 

potential labor savings at closely spaced 

wells. Several nearby wells can be instrumented and transmitted using a single 

DCP. Some USGS offices take advantage 

of existing surface-water instrumentation 

to transmit ground-water data. 

Example Real-Time Applications 

Across the Nation

Real-time ground-water monitoring is 

used effectively in many areas of the 

Nation.

Florida

Although Florida is blessed with abundant rainfall, large annual variations in 

precipitation result in water shortages, 

particularly during the dry winter months. 

Parts of Florida have been under drought 

conditions since October 1998, and 2000 

was the driest year in at least 85 years 

in the 16-county Southwest Florida Water 

Management District. Because Florida 

State and local water managers have 

anticipated these climatic conditions, the 

USGS offices in Tampa and Miami maintain a network of more than 130 wells 

with real-time instrumentation. Data from 

With this method, water-level data are 

recorded by a data-collection platform 

(DCP) and transmitted, often on a 

4-hour schedule, by satellite telemetry 

to a USGS ground station. These data 

then are displayed over the Internet at 

http://water.usgs.gov/nwis/gw. 

In October 2001, real-time groundwater data from at least 582 wells were 

being served from 35 States and Puerto 

Rico. The largest percentage (23 percent) 

of the wells were in Florida, and 6 States 

(Florida, Pennsylvania, Texas, North Carolina, Kansas, and Missouri) served nearly 

75 percent of the wells with real-time 

instrumentation.

Why Real-Time Data?

Real-time ground-water data have 

many inherent advantages over data 

collected and distributed by traditional 

means. These advantages can be grouped 

into four categories: timeliness, data quality, data availability, and cost.

1. Timeliness—The most apparent benefit of real-time ground-water data is the 

ability to provide timely data for groundwater management. Most commonly, this 

is during drought conditions. Real-time 

ground-water data also can be used to 

monitor high water levels (ground-water 

flooding), to manage well fields, and to 

trigger ground-water sampling.

2. Data Quality—Real-time data collection and management improve the quality of continuous data. In contrast to 

traditional continuous data, which are 

retrieved on a monthly (or longer) schedule, real-time data are reviewed daily, 

and equipment malfunctions are identified 

quickly. Missing or poor quality data can 

be reduced substantially. 

“Real time and historical streamflow 

data....are a resource to the nation and

represent the type of data presentation we 

would like to see for groundwater data....”

National Research Council, 2000,

“Investigating Groundwater Systems on

Regional and National Scales”

Real-time data collection and transmission 

system.

GOES

 Satellite

Ground

receiver

Data-collection station

platform

installation

Well

U.S. Geological

Survey office

U.S. Department of the Interior

U.S. Geological Survey

USGS Fact Sheet 090–01

December 2001

Real-Time Ground-Water Data for the Nation
these wells are used daily by the regulatory staff in Florida Water Management 

Districts to make decisions on water use 

(http://www.sfwmd.gov/). The South Florida Water Management District has chosen 

ground-water levels “...as the primary 

drought indicator because ground water 

responds more slowly to rainfall than surface waters....” Water-level data from these 

wells also have been used by the National 

Weather Service to characterize antecedent 

conditions for flood predictions.

Pennsylvania

In 1931, a statewide well network was 

established in Pennsylvania to monitor 

water-level fluctuations as a result of interest in ground-water-level declines resulting from the drought of 1930. Today, 

this network consists of about 70 wells 

operated by USGS in cooperation with 

the Pennsylvania Department of Environmental Protection. The Commonwealth 

Drought Coordinator uses data from the 

wells when categorizing counties for a 

drought declaration. Presently, groundwater levels for nearly 70 network wells 

are transmitted by satellite telemetry 

and displayed on the USGS Web pages 

for Pennsylvania. Recently, the Pennsylvania Office has added 30-day moving 

average water levels and State-regulated 

drought levels to their data presentation 

(http://pa.water.usgs.gov/pa_duration.html).

Texas

In response to the drought of 1996, 

the Texas Legislature passed Texas Senate 

Bill 1 in 1997, a comprehensive waterplanning law dividing Texas into 16 waterplanning regions. This legislation requires 

regions to produce plans to address needs 

during periods when ground-water levels 

are 50- and 75-percent of normal. To 

help meet this requirement, about 45 wells 

within the State ground-water network are 

instrumented with satellite telemetry. The 

Texas Water Development Board and local 

governments use the real-time groundwater data to manage water during periods 

of drought. 

Well “J17” near San Antonio is completed in the Edwards aquifer, the sole 

source of supply for the city. Water 

levels from this well are shown daily 

during weather reports on the local news 

stations. During November 2000, when 

water restrictions were prevalent in the San 

Antonio area, data from this well were 

served more than 11,000 times over the 

Internet. 

North Carolina

Nutrient loading to estuaries is a 

critical concern in North Carolina. To help 

define nutrient sources, the USGS North 

Carolina Office has a program to sample 

discharge from tile drains on Coastal Plain 

farms. Real-time ground-water data from 

a nearby well are used to plan sampling 

events from the tile drains. Prior to the 

availability of real-time data, predicting 

when ground-water levels would be high 

enough to produce flows in the tile drains 

would have been difficult. The use of realtime data has eliminated field trips that 

were wasted because tile drains were dry. 

Kansas

Water-level data have been collected 

since 1992 from wells and streams in the 

Kansas River Valley and upland areas of 

Fort Riley, Kansas. Because of the complex nature of the ground-water system, 

continuous water-level measurements are 

needed to evaluate ground-water flow and 

potential contaminant transport at Fort 

Riley. Approximately 30 DCP’s have been 

installed to monitor ground-water levels at 

56 wells. These data are used with surfacewater data to determine ground-water and 

surface-water interactions. When wells 

are too far from the surface-water gage for 

direct electrical connection of instrumentation, the USGS Kansas Office has installed 

RF systems to relay ground-water data to 

the DCP at the nearby gaging station for 

transmission to the office by telemetry. 

DCP’s were selected for this investigation 

because they provide high-quality data and 

because of access restrictions at Fort Riley 

(Myers and others, 1999). 

In conclusion, real-time ground-waterlevel data meet a critical need throughout 

the year under many circumstances, not 

just during drought. Real-time data applications allow effective aquifer management, produce high-quality data, and can 

be cost effective. As the availability and 

reliability of real-time ground-water data 

increase, so too will the value to scientists 

and the public alike.

—William L. Cunningham

Reference

Myers, N.C., Finnegan, P.J., and Breedlove, 

J.D., 1999, Analysis of water-level data and 

ground-water flow modeling at Fort Riley, 

Kansas: U.S. Geological Survey WaterResources Investigations Report 99–4115,

6 p.

For additional information about real-time 

ground-water data, please see 

http://water.usgs.gov/nwis/gw

or contact:

Office of Ground Water

U.S. Geological Survey

411 National Center

12201 Sunrise Valley Drive

Reston, Virginia 20192

(703) 648–5001

“toyed with the idea of going with a flood 

watch...but looked at the USGS ground 

water plots and these values were relatively low. Thus decided in not issuing 

a flood watch.”

National Weather Service Area Forecast

Discussion, Miami, Florida

September 19, 2000 

Hydrograph illustrating 30-day moving average 

of depth to water as compared to historical data, 

Well UN-51, Union County, Pennsylvania.

Daily water-level report during local weather 

forecast, KSAT Channel 12,

San Antonio, Texas (by permission).

Multiple Sensor data-collection platform (DCP) 

installation in Kansas.

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30-DAY MOVING AVERAGE DEPTH TO

WATER, IN FEET BELOW LAND SURFACE

2000 2001

J F MA MJ J A S O N D J F MA MJ J A S O N D

30-day moving average of current daily depth to water

25th to 75th percentile depths (normal conditions)

10th to 25th percentile depths (drought watch conditions)

5th to 10th percentile depths (drought warning conditions)

0 to 5th percentile depths (drought emergency conditions)

EXPLANATION