Measuring and Monitoring Water

We think of groundwater as moving slowly, and groundwater quality as changing slowly—over decades or even centuries. But in some parts of some aquifers, groundwater quality can fluctuate rapidly, sometimes over just a few hours. Are such changes part of a long-term trend, or just part of a short-term cycle? And what does that mean for suitability for drinking?

Groundwater provides nearly one-half of the Nation’s drinking water, and sustains the steady flow of streams and rivers and the ecological systems that depend on that flow. Unless we drill a well, how can we know the quality of the groundwater below? Learn about how the USGS is using sophisticated techniques to predict groundwater quality and view national maps of groundwater quality.

More than 100 million people in the United States—about 35 percent of the population—receive their drinking water from public-supply wells. These systems can be vulnerable to contamination from naturally occurring constituents, such as radon, uranium and arsenic, and from commonly used manmade chemicals, such as fertilizers, pesticides, solvents, and gasoline hydrocarbons. Learn about the...

The age of groundwater is key in predicting which contaminants it might contain. There are many tracers and techniques that allow us to estimate the age—or mix of ages—of the groundwater we depend on as a drinking water supply.

Research by the USGS National Water Quality Assessment (NAWQA) Project on water quality of rivers and streams covers a broad range of topics, from nonpoint pollution issues to vulnerability of aquatic ecosystems. Dive in and find out more about current water-quality conditions, how and where water quality is changing, and the latest information on pesticides, nutrients, and other contaminants.

These tables, maps, and graphs provide estimates of U.S. agricultural pesticide use suitable for evaluating national and regional patterns and trends of annual pesticide use.

Sediment cores let us look back in time at the contaminant history of a watershed. Learn about what lake and reservoir sediment cores tell us about trends in metals, organochlorine pesticides, polycyclic aromatic hydrocarbons, and other sediment-related contaminants.

Volatile organic compounds (VOCs) are chemicals that both vaporize into air and dissolve in water. VOCs are pervasive in daily life, because they’re used in industry, agriculture, transportation, and day-to-day activities around the home. Once released into groundwater, many VOCs are persistent and can migrate to drinking-water supply wells.

The redox state of groundwater—whether the groundwater is oxic (oxidized) or anoxic (reduced)—has profound implications for groundwater quality. Knowing the redox conditions of groundwater can help determine whether it contains elevated levels of many contaminants, including arsenic, nitrate, and even some manmade contaminants.

What is SPARROW? SPARROW (SPAtially Referenced Regression On Watershed attributes) is a watershed modeling technique for relating water-quality measurements made at a network of monitoring stations to attributes of the watersheds such as contaminant sources and environmental factors that affect rates of delivery to streams and in-stream processing. The core of the model consists of a nonlinear...

Selenium (Se) as a contaminant of ecosystems is bioaccumulative and causes reproductive effects in fish and wildlife. Ecosystem-scale Se modeling predicts Se bioaccumulation based on dietary biodynamics within site-specific food webs. The model can be used to forecast Se toxicity under different management or regulatory proposals or to translate a tissue guideline to a dissolved guideline.

In 1991, Congress established the National Water-Quality Assessment (NAWQA) Project to address where, when, why, and how the Nation's water quality has changed, or is likely to change in the future, in response to human activities and natural factors. This page discusses the first two decadal cycles of NAWQA research from 1991 through 2012.