The Quality Difference between Water Supplies in Urban Area and Rural Area

Which area has the better water quality? Urban or rural? The answer to this is not simple. On one hand, it can be said that the quality of water in rural areas is better. As rural areas are removed from industrial activities or urban runoff that may result in the degradation of the quality of river water, lake water, or groundwater. However, there are still many exceptions. In areas with intensive agricultural activity, mining, and logging, the impacts on water quality can be severe on rural waters.


Over the past 10 years Concerns about the potential impact of farm production on the quality of the Nation’s rural drinking and recreational water resources have risen over the past 10 years. Agricultural sources are now the largest single contributor to the Nation’s surface water quality problem, and there is evidence that some ground water supplies may be vulnerable to leaching chemicals in agricultural areas. This report explores the use of nonmarket valuation methods, such as travel cost to a recreational lake, to estimate the benefits of improving or protecting rural water quality from agricultural sources of pollution. Food and fiber production can impair surface and ground water resources. Fertilizers and pesticides used to grow crops may leach through soils and contaminate ground water supplies. Dissolved chemicals in drinking water may then pose a human health risk. Runoff of chemicals from sediment and cropland, as well as soil erosion, may impair the quality of streams, lakes, rivers, and wetlands.

Most early efforts to protect water quality were directed at municipal and industrial sources of pollution, where a single pollutant source could be identified (point-source pollution). The cumulative effect of more than 20 years of investment in such point-source pollution control is that non-point-source pollution, particularly from agricultural sources, has become the largest single remaining water-quality problem in the Nation. Both public and private costs are relevant in resolving conflicts between agriculture and water quality. When making production decisions, farmers balance their expected production costs with expected returns from crops produced. However, farmers’ decisions may have unintended long-range effects. Economic losses from impaired water quality reflect, in part, how important the resources are to society. One case study is used to illustrate the relationship between agricultural production and the costs of impaired surface water quality. Changes in farm production practices may lead to changes in the quality of nearby lakes, affecting recreation activities.

While rural water has its challenges coming largely from intensive agricultural demands, urban water faces it's challenges as well. The largest challenge? It's called stormwater, or urban runoff. Urban runoff pollutants are many and varied depending on the land uses and pollutant sources present in an urban area. Typically loadings of urban pollutants are greatest from industrial and commercial areas, roads and freeways, and higher density residential areas. Although sources of specific pollutants may vary widely in urban areas, motor vehicles are recognized to be a major source of pollutants, contributing oils, greases, hydrocarbons, and toxic metals. The more cars and trucks we have, and the more streets and parking lots we build to accommodate these vehicles, the greater the concentration of urban runoff pollutants and the more money we have to spend managing these pollutants. In addition to the NURP studies (U.S. EPA, 1983), several other publications provide excellent reviews of urban stormwater quality (Make peace et al., 1995; Pitt et al., 1995).

Major categories of urban pollutants include sediments, nutrients, microbes, and toxic metals and organics. Sediment concentrations in urban runoff are particularly problematic because of their ubiquitous nature, and the fact that many other pollutants occur in a solid-state associated with sediment particles. Sediment loadings occur primarily from soil erosion and runoff from construction sites in urban areas. Road sanding can also be a major source of sediments. Increased sediment in urban runoff may cause significant biological, chemical, and physical changes in receiving waters including loss of water clarity, clogging of gills and filters of aquatic organisms, and aquatic habitat degradation including the smothering of spawning beds and benthic communities. Sources of nutrients such as nitrates and phosphates include chemical fertilizers applied to landscaped areas, lawns, and gardens, failed septic systems, soil erosion, and atmospheric deposition. Excessive nutrients in urban runoff can stimulate algal growth and cause nuisance algal blooms.

Urban runoff may also contain high levels of organic matter that can lead to depleted oxygen levels in water and sediment when it decomposes. This in turn may cause excessive odors and fish deaths in receiving waters. Microbes include hundreds of different kinds of bacteria, protozoa, and viruses that are ubiquitous in the natural environment. Many are beneficial, while others can cause diseases in aquatic biota, and illness or even death in humans. Some types of microbes are pathogenic (e.g., Giardia spp.), while others indicate a potential risk for water contamination (e.g., fecal coliform bacteria) and may limit swimming, boating, and consumption of fish and shellfish in receiving waters. Microbes are almost always found in high concentrations in urban stormwater, but are highly variable in nature and very difficult to eliminate.

Primary sources of microbes include failed septic systems, and waste products from pets, birds, and wild mammals commonly found in urban areas. Toxic pollutants commonly found in urban runoff include trace metals such as lead, copper, zinc, and organic compounds including oils, grease, phthalates, and chlorinated hydrocarbons. Copper, lead, and zinc were detected in more than 90% of stormwater samples from the NURP studies, and 14 toxic organic compounds were detected in more than 10% of the samples (U.S. EPA, 1983). Sources of toxics include the breakdown of metal products, vehicle fuels and fluids, vehicle wear, industrial processes, and the use of industrial and household chemicals such as paints, preservatives, and pesticides. Trace metals and organic compounds may be highly toxic to aquatic organisms and can bioaccumulate in fish and shellfish.

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