The definition of water quality is not objective, but is socially defined depending on the desired use of water. Different uses require different standards of water quality.
- Water used for hydropower generation, industrial purposes, and transportation does not require high standards of purity.
- Such uses as recreation, fishing, drinking, and habitat for aquatic organisms rely on higher levels of water quality.
For that reason, water quality should be taken to mean the “physical, chemical, and biological characteristics of water necessary to sustain desired water uses.”
Monitoring the quality of water is important because clean water is necessary for human health and the integrity of aquatic ecosystems.
Ecosystems filter and cleanse water. This ability, however, is being impaired by pollution and habitat degradation in many rivers, lakes, and estuaries around the world.
The following summarizes key findings of the PAGE study regarding the condition of freshwater systems, as well as the quality and availability of data. For the full PAGE analysis on water quality in freshwater systems, download the full chapter in PDF.
Conditions and trends
-
Water-borne diseases from fecal contamination of surface waters continue to be a major cause of mortality and morbidity in the developing world.
-
Surface water quality has improved in the United States and western Europe in the past 20 years with respect to some pollutants; however, nutrient loading from agricultural runoff continues to be a problem in these two regions.
-
Worldwide water quality conditions appear to have degraded in almost all regions with intensive agriculture and large urban/industrial areas.
-
Cases of algal blooms and eutrophication are being documented more frequently in most inland water systems around the world.
-
Of the 82 major river basins in the world, those in North America, Europe, and Africa had the highest concentration of organic matter for the period 1976-90.
-
Phosphorous concentration in U.S. waterways show improvement, whereas nitrate concentrations have remained more or less stable for the 1980-89 period.
-
Evidence shows that nitrate pollution in groundwater, from fertilizer use, is getting worse in northern China, India, and Europe. Population increases in these areas and the need to increase agricultural production will require increase use of fertilizers, which will exacerbate the groundwater pollution problem.
Information status and needs
-
Data on water quality at the global level is very scarce. There have been very few sustained programs to monitor water quality worldwide.
-
Information is usually limited to industrial countries or small, localized areas.
-
Water monitoring is also almost exclusively limited to chemical pollution rather than biological monitoring, which would provide a better understanding of the condition of the system. For regions, such as Europe, where some monitoring is taking place, difference in measures and approaches make the data hard to compare.
Quality and availability of data
PAGE measures and indicators
Data sources and comments
Global concentrations of biochemical oxygen demand (BOD), phosphorous, and nitrates by river basin Data are from
UNEP/GEMS (United Nations Environment Program Global Environment Monitoring System/Water). 1995. Water Quality of World River Basins. Nairobi, Kenya: UNEP.
This project measured water quality in 82 major river basins from 1976 to 1990. Measurements are from a network of 175 sampling stations in around 60 countries. Because data from sampling points are extrapolated to the entire watershed, these data should be interpreted with caution.
Trends in phosphorous and nutrient concentrations in Europe and the United States Data for Europe are from
EEA (European Environment Agency). 1994. European Rivers and Lakes: Assessment of Their Environmental State. P. Kristensen and H. O. Hansen, eds., EEA Environmental Monographs 1, National Environmental Research Institute, Copenhagen, Denmark: Danish Ministry of Environment and Energy.
Data for the United States are from the U.S. Geological Survey (USGS) National Water-Quality Assessment (NAWQA) program, and the USGS National Stream Quality Accounting Network (NASQAN).
USGS (U.S. Geological Survey). 1999. The Quality of Our Nation’s Waters — Nutrients and Pesticides. USGS Circular 1225. Reston, Virginia, U.S.A.: USGS.
NASQAN monitors water quality in the four largest river systems in the United States: the Mississippi (including the Missouri and Ohio), the Columbia, the Colorado, and the Rio Grande. NAWQA performs detailed studies in 60 smaller basins across the United States, including Alaska and Hawaii.
Biological methods of water quality monitoring Data are from studies from around the world, including the United States, France, India, the United Kingdom, and Australia. All studies illustrate applications of biological criteria to monitor water quality.
Nitrate pollution in groundwater Data are from various sources and studies for China, India, western Europe, and the United States.
