Water Quality

RCA Issue Brief #9 March 1996

Cleaning up the water
How does water pollution occur?
Water quality standards
Agriculture's role in water quality
What farmers and ranchers are doing to protect water quality
Water quality partnerships
Water quality depends on soil quality

Did you know ...

...that although 70 percent of the Earth's surface is water, 97 percent of that is in oceans and estuaries and not available for drinking or irrigating? And that much of the remaining 3 percent is trapped in glacial ice?

...that the volume of water on Earth stays the same, but the form--liquid, gas, or solid--changes constantly?

...that per-capita daily water use in the United States is about 1,400 gallons (all uses, including irrigating, mining, and manufacturing, as well as domestic use)? Per-capita daily water use in other countries ranges from 5 gallons in Haiti to well over 3,000 gallons in Iraq, with a worldwide average of 475 gallons.

...that one American in six draws his or her drinking water from private wells and springs? And that many of these private water sources are not tested for water quality?

...that soil quality is a key determinant of water quality because soils regulate and partition water flow and buffer against human use and environmental changes?

...that the risks associated with water pollution can be measured both in terms of hazard (technical risks, such as getting cancer because of what's in the water) and in terms of outrage (public reaction to the pres-ence of pollutants, usually synthetic chemicals, without regard to hazard)?

...that many of the contaminants that people introduce into water--such as nitrate--also occur naturally?

...and that three out of four farmers have changed their farming practices to help reduce water pollution?


Water quality is a moving target, depending on the water's intended or designated uses. For a water quality problem to exist, the water must be impaired for one or more uses, such as drinking water supply, fishing, recreation, wildlife habitat, livestock, or irrigation.

Water quality problems may be localized--such as a fish kill in a pond. Or they may be regional, national, or international in scope. Water quality impairment in Lake Erie, for example, affects recreation, drinking water, commercial fishing, and other uses in both the United States and Canada.

Cleaning up the water

By 1970, water pollution had captured the public's attention as a serious problem in the United States. One classic example of polluted water was Cleveland's Cuyahoga River, which actually caught fire. The response to this and other horror stories was the Clean Water Act, passed in 1972 with the goal of making rivers, lakes, and coastal waters fishable and swimmable by 1985.

Although our Nation hasn't yet achieved this goal, we have made great progress. Thanks largely to controls on point sources of pollution--factories, sewage treatment plants, and other facilities that discharge pollutants directly into the water--1 billion fewer pounds of toxic pollutants enter our waterways each year.

However, many of the Nation's rivers, lakes, and estuaries are still not fully safe for swimming or fishing. Industry is still responsible for some pollution; however, much of today's water pollution occurs because of runoff from nonpoint sources--city streets, parking lots, farms, construction sites, and logging and mining operations. Pollutants in such runoff include sediment; pesticides and fertilizers from agriculture, lawns, parks, and golf courses; and oil, grease, salt, and chemicals from urban sources. Precipitation, likewise, carries pollutants in the form of acid rain in some parts of the country and also brings airborne nitrogen and carbon to Earth. This kind of water pollution, called nonpoint source pollution, affects both surface water and ground water and is far harder to control than point source pollution simply because the origin of the contaminants cannot be pinpointed.

How does water pollution occur?

Water quality is impaired when a pollutant or pollutants enter a water body and limit its use for drinking, fishing, swimming, or some other purpose. Pollutants enter or are delivered to a water body through a process called "loading." Nonpoint source loading begins with the availability of pollutants: Tilled soil is exposed, pesticides are applied, or animal waste is spread on the land, for example. These available pollutants are then detached (as when the impact of raindrops dislodges soil particles), adsorbed (pesticides adhere to clay particles, for example), or dissolved by rainfall or snowmelt, which then carries the detached, adsorbed, and dissolved pollutants over the land to nearby surface water bodies, or through the soil into ground water. The major pollutants resulting from agricultural activities are nutrients, sediment, animal manures, pesticides, and salts, but these substances can come from other sources as well.

Management practices reduce pollution where they decrease the availability of the pollutants; prevent their detachment, adsorption, or dissolution; or interrupt the transport process. Reducing the availability of pollutants is the first step in pollution prevention--an important step in protecting the quality of both surface water and ground water.

pollution process graphic

Water quality standards

The most comprehensive evaluations of the extent of point and nonpoint source water contamination in surface water are State assessments prepared under authority of Section 305(b) of the Clean Water Act. States and Tribal governments designate uses for each water body--such as swimming, fishing, irrigating, or drinking--and adopt criteria to protect the designated uses.

The States and Tribes report their assessments of water quality to the U.S. Environmental Protection Agency in a form known as a 305(b) report, as follows:

  • States and Tribes are required to designate uses consistent with the ''fishable/swimmable'' goal of the Clean Water Act. They then set water quality standards that include designated uses, criteria to support those uses, and an antidegradation policy and method for implementing it.
  • Water designated for use as drinking water typically has a higher standard, or different criteria, than water designated for agricultural use. Substances that occur naturally in water, such as phosphate or nitrate, are considered pollutants only when their concentrations in the water are high enough to cause health or environmental problems.
  • States and Tribes set standards for water and define the condition of some portion of the assessed waters in quantifiable physical, chemical, or biological terms.
  • Waters not supporting uses, partially supporting uses, or for which uses are considered threatened are assessed to determine the sources of pollution, such as urban runoff, agriculture, or point sources, and the causes of impairments or threats, such as nutrients, sediment, or habitat modification.

Agriculture's role in water quality

The most recent State assessments indicate that nearly two-thirds of assessed water bodies in the United States support their designated uses. In addition, because not all waters are assessed for each biennial 305(b) report, the full extent of agriculture's contribution to water quality impairment is not known. In 1994, where States reported sources of impairment, agriculture was a contributing source for 60 percent of the impaired river miles and 50 percent of the impaired lake area--more than any other single source. Agriculture was a contributing source for 34 percent of impaired estuary area. States identified agriculture as a major source of impairment for 25 percent of impaired river miles, 10 percent of impaired lake areas, and 6 percent of impaired estuary areas. Where agriculture is a source of impairment, the two most prevalent pollutants are sediment and nutrients.

charts showing agriculture's effects on water quality

What farmers and ranchers are doing to protect water quality

America's farmers and ranchers produce the food and fiber that sustains us all. Agricultural production, however, uses water, requires the addition of soil amendments such as fertilizer, and in many places entails the use of synthetic chemicals to control weeds, insects, and other pests. As a consequence, agricultural lands can contribute to nonpoint source water pollution if proper management practices are not used.

Because too much of an agricultural input in the wrong place can cause water quality degradation or other environmental problems, management practices and systems have been developed that can sustain yields and protect the natural resources that produce them. The key is to reduce pollutant loadings by interrupting the process at the point of availability, detachment, or transport. Nearly 75 percent of farmers have already changed some farming practices to help reduce the delivery of nonpoint source pollutants. Unfortunately, sometimes even when farmers do everything right, forces beyond their control--the Midwestern floods of 1993, for example--can carry pollutants into the environment.

Farmers and ranchers are reducing potential pollutants by decreasing the availability of:

  • soil to become sediment, primarily through the use of agronomic practices such as cover crops, residue management, and rotations that include close-grown crops;
  • nutrients for transport, by accounting for all nutrients available, regardless of source, method of incorporation, and application rate and timing;
  • pesticides through integrated pest management, including crop rotations, cultivation, biological pest control, scouting, and selecting pesticides that are more environmentally friendly, as well as through reducing the use of pesticides in their operations;
  • salt through irrigation water management, including application, timing, and amount;
  • heavy metals by controlling soil acidity, monitoring, and limiting quantities and locations for sludge application; and
  • pathogens by minimizing surface runoff, detachment, and transport; excluding livestock from surface waters; using buffer strips in riparian areas; and properly disposing of dead animals.

Producers must consider the relative merits of permanent practices that have high capital costs versus those that have lower capital costs but require careful continuous management. Practices that solve one water quality problem must not increase the potential for another. For example, conservation practices that increase infiltration may also increase the volume of water-soluble nutrients and pesticides reaching ground water.

Even where there is no known water quality problem, the Natural Resources Conservation Service recommends that farmers and ranchers integrate water quality protection into all of their planning and operations through a whole-farm, ecosystem planning approach. Water quality problems are best solved or prevented on a watershed-wide basis where individual producers' operations contribute to meeting larger area goals for clean water.

Water quality partnerships

In 1989, USDA made a commitment to help protect the Nation's water from contamination by agricultural chemicals and waste products by establishing the Water Quality Program (WQP). This program builds upon past experimental efforts, including the Model Implementation Program of the 1970's and the Rural Clean Water Program and Water Quality Special Projects of the 1980's. The WQP is carried out through research and development; educational, technical, and financial assistance; and data base development and evaluation.

USDA is working with other Federal agencies, State and local agencies and organizations, and industry to help farmers and ranchers reduce agricultural pollutants in waters nationwide. Hydrologic unit area (HUA) projects, demonstration projects, and regional projects are the Department's primary vehicles for increasing applied knowledge of how and why agricultural pollution occurs--and of what can be done to arrest such pollution.

The 74 HUA projects aim to reduce nonpoint source pollution associated with crop and livestock production. Among the specific targets of these projects are dairy manure, runoff associated with production of turf and ornamental plants, poultry manure and other by-products, excessive nutrients applied to row crops, and inefficient irrigation systems.

The 16 water quality demonstration projects use science-based information to show new practices for which research is often ongoing. These projects showcase innovative conservation practices and technologies and promote their use outside the project.

Ten Management Systems Evaluation Area (MSEA) sites in the Midwest are testing grounds for an interagency research and outreach program to improve our understanding of how current farming systems affect water quality, to propose modifications to those systems, and to transfer new technology and methods to farmers for use on the land.

Accelerated technical assistance and information in seven regional projects is hastening development of nonpoint source management plans. These projects encompass the Chesapeake Bay, Colorado River Basin, Great Lakes, Gulf of Mexico, Tennessee Valley, and Lake Champlain, as well as the U.S. Environmental Protection Agency's National Estuary Program.

As progress is made through the WQP projects, a measure of the impact these efforts have on water quality would be valuable. Such measurements will provide insights on progress in meeting goals of the Clean Water Act. The National Water-Quality Assessment (NAWQA) program of the U.S. Geological Survey aims to provide a nationally consistent description of current water quality conditions for a large part of the Nation's water resources; to define long-term water quality trends where possible; and to identify, describe, and explain these conditions and trends. USGS conducts investigations in 60 study areas throughout the Nation representing a variety of geologic, hydro- logic, climatic, and cultural conditions. These studies are building blocks for understanding regional differences in physical, chemical, and biological characteristics of the Nation's ground and surface waters.

USGS communications and coordination with USDA and other Federal agencies, State agencies, and organizations contribute to NAWQA's success.

maps showing the location of water quality related projects

Water quality depends on soil quality

Good quality water reflects what we do on the land as well as what we do in the water. Because agriculture is by far the most extensive land use in the United States, improved water quality depends in large part on the commitment of American farmers and ranchers to improving the quality of soil and other natural resources as well as water. The improvements in water quality we've already seen reflect that commitment in action. Agriculture's contribution to water quality impairment will likely continue declining as whole-farm planning creates a more ecologically aware farming environment, thus enhancing the environment as a whole.

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