Hydrology and water use are considered from a variety of perspectives including social, economic, legal, scientific, and environmental to determine how differing viewpoints affect the quality and quantity of water supplies. Researchers study pollution carried by water, which includes oceans, rivers, streams, rain, snow, and ice, and devise methods to clean and control it. Some study weather-related problems such as flood forecasting, drought management, acid rain, and global warming. Others manage water resources so that the goals of all water users are achieved efficiently while protecting the environment. In order to adequately extenuate and manage water quality issues, they must be dealt with from all perspectives. Some water quality problems that can be common to entire regions include toxic contamination from industry, waste disposal, and eutrophication from human sewage. Bacterial pollution of water supplies is a perpetual dilemma with adverse effects on human health. The major concerns centered upon high bacterial and organic loads range from poor-quality drinking water, eutrophication, and disappearance of aquatic life to food contamination and the prevalence of waterborne diseases.
Rivers can be polluted from a number of different sources. The largest contributors include industrial and urban wastewaters from large cities, wastewater from mining industries, and agricultural runoff. As a result, many river water resources today are chemically and biologically contaminated. Large quantities of agricultural contaminants are likewise disposed of in streams flowing to the sea, where there has been found clear evidence of elevated levels of phosphorous, nitrates, potassium, PCBs, pesticides such as Dichlorodiphenyltrichloroethane (DDT), and highly organic effluents. These elevated levels of pollutant concentrations caused by the indiscriminate discharge of highly pollutant-loaded effluents into water bodies are also seen in deep underground aquifers, which are often contaminated through the same negligent processes.
Experiences over the past century have contained many useful lessons that are now being utilized to shape water management practices in an effort to effectively address the threats of water shortages and pollution that are growing worldwide. A half-century ago, water resources planning focused on building facilities to capture and deliver water for beneficial uses and to contain floods to reduce damages. Planners were certain that full resource development would foster economic growth and serve broad social needs. Governments built projects that proved financially costly, environmentally destructive, and politically divisive. Environmental harms increased as projects drained rivers and wetlands and converted forests, meadows, and deserts into fields and cities. Political differences deepened as jurisdictions sought to develop their own water resources with little regard for the needs of neighbors. Disputes mounted among towns, states, and nations. As the water resources were more fully developed, projects became larger and more costly, and their adverse environmental impacts became more severe. Fiscal and environmental concerns caused the political process to halt construction as society looked for alternative approaches to meeting basic human needs. Now, water withdrawals are approaching the upper limit of what nature can supply and fresh water resources are being reduced by pollution and threatened by climate change.
Throughout history, humans have been concerned with the proper management of hydrological resources. This task has been less than facile simply because water availability and population-induced threats vary greatly among locations and over time. There is a need to think more creatively to gain deeper understanding of the inherent heterogeneities and diversities contained within hydrological systems. Proper management of water resources will need to address the problems and challenges of growing regional and global populations with complex societies, but will also need to sustain the needs of the Earth’s natural ecosystems.