- Water Quality
- Effect of Contaminants on Water Quality
- Water Quality Standards
- Water quality monitoring
The term “water quality” describes the physical, chemical, biological and aesthetic properties of water which determine its fitness for a variety of uses and for protecting the health and integrity of aquatic ecosystems. Many of these properties are controlled or influenced by constituents which are either dissolved or suspended in water. “Water quality standards” include numerical parameters established nationwide (in form of laws, decrees) to control water quality for specific types of water management.
Many different water quality criteria and guidelines have been published in the international and local literature. Different approaches and methodologies have often been used to derive criteria and guidelines, for example, some guidelines specify maximum concentrations for constituents fit for use, whereas others attempt to define the ideal concentration of a constituent, often with the inclusion of safety factors.
The most common standards used to assess water quality are related to drinking water, safety of human contact and health of ecosystems. These standards are the portion of the rule that defines the acceptable amount of a constituent in water and are developed by regulatory agencies in order to protect human health. Water quality goals are typically more stringent than standards and may include constituents not covered by regulations but of particular importance to the goal-setting entity.
As analytical techniques for measuring constituents in water have become more sophisticated and knowledge of how human health is impacted has grown, standards and regulations have become even more stringent, meaning more constituents are regulated and at lower concentrations.
The ideal method for establishing standards involves a scientific determination of health risks or benefits, a technical/engineering estimate of costs to meet various water quality levels and a regulatory/political decision that weights benefits and costs to set the standard.
Many factors affect the quality of surface and groundwater. Water moving over or under the land surface can undergo physical and chemical changes. These changes may be caused by either natural factors or human activities.
Contaminants can impair water quality and affect water use. A contaminant is an undesirable substance in water that either is not normally present or is a naturally occurring substance at an unusually high concentration.
Contaminants can be divided into four general classes: sediment and natural organic materials, nutrients, bacteria and toxic substances. These can contribute to water by either point or non-point sources. Point sources contribute contaminants at a discrete site, such as the outflow from a pipe, ditch, tunnel, well or concentrated animal-feeding operation. These sources can be controlled to some degree by treatment at or before the point of discharge. Non-point sources contribute contaminants from a broad area; as a result, such sources are not as easily identified or controlled as point sources. Non-point sources include the atmosphere, agricultural areas, golf courses, residential developments, roads, parking lots and contributions from groundwater along lengthy reaches of streams.
Sediment and Natural Organic Materials
Sediment is defined as particles derived from soil, rock, or organic matter that have been, or are being, transported by water or wind. Natural organic materials include plant debris, and human and animal wastes. The erosion of land surfaces and stream banks produces sediment. Erosion occurs naturally, but human activities, like farming, logging, or road construction can increase sediment transport to and within streams.
Sediment deposited in streams can restrict navigation. Sediment can also increase the potential for floods by decreasing reservoir storage and stream-channel capacity. Suspended sediments contribute to the reduction of water clarity and quality. Fine sediments can severely alter aquatic communities by clogging fish gills and suffocating fish eggs . Harmful materials such as heavy metals and toxic chemicals can attach to sediments and move with them down the stream system.
Nutrients are any organic or inorganic compound needed to sustain life. Examples include carbon, nitrogen, phosphorus and potassium. Nutrients are contributed to waters from the atmosphere, agricultural lands, golf courses, lawns, wastewater treatment plants, and factories.
An excess amount of nutrients in water can result in a disproportionate amount of aquatic vegetation. The decomposition of this excess vegetation can remove oxygen from water and cause fish and other aquatic life to die. It is mentioned that high nitrate or ammonia concentrations can impact drinking water. Figure 1 shows algal blooms developed when water nutrient levels are high enough to support rampant growth.
Figure 1: Algal blooms developed when high nutrient levels exist
Some bacteria are disease-causing organisms that may be delivered to surface water and groundwater by sewer overflows, leaking septic tanks and runoff from animal feedlots or pastures. Some bacteria are a threat to humans, and indicator organisms such as fecal coliform are used to determine their presence. Indicator bacteria are found in great numbers in the intestines of humans and other warmblooded animals.
In sufficient quantities, toxic substances, such as cleaning solvents, pesticides and certain metals, can cause sickness, genetic disorders and even kill organisms. Toxic chemicals can enter waters through direct discharge from industry or by improper disposal of industrial, mining, farm, and household wastes. Contaminants contributed from industrial uses of water include toxic substances produced from cleaning solvents, acids, and alkalis.
Even extremely low concentrations of some chemicals are hazardous to humans and aquatic life. Toxic substances also can affect an organism’s growth, metabolism, reproduction or behavior (Vandas, et al., 2002).
The effect that a contaminant has on water depends upon the characteristics of the water itself and the quantity and characteristics of the contaminant. Each body of water can be described according to its physical, chemical, and biological characteristics. Collectively, these characteristics give each water body an ability to absorb or assimilate some contaminants without becoming degraded. For example, large streams can absorb a larger quantity of a contaminant than a small stream.
Many human activities can alter or impair the quality of the water. Commonly, these activities increase the concentrations of dissolved or suspended contaminants, change the acidity of receiving waters, and/or increase the water temperature.
The degree to which human activities have altered the water quality of a particular stream or aquifer can commonly be determined by sampling and comparing the water chemistry and biota of the impacted system with the chemistry and biota from a nearby area that is not impacted by humans. The chemistry of the non-impacted water is called the background chemistry.
The quantity of contaminants reaching water sources is dependent upon many factors including land management practices, watershed characteristics, chemical properties of the contaminant and the amount of the contaminant that is released to the environment.
Streams and shallow unconfined aquifers are more vulnerable to contamination than water in deep aquifers. Confined aquifers generally are buried deeper beneath the land surface and are protected by layers of relatively impermeable materials that impede the movement of contaminated water from the land surface.
Groundwater contamination is extremely difficult to reverse in part due to the slow rate at which water moves through aquifers. Some pesticides have the potential to harm humans, wildlife and native plants if they are exposed to high enough levels for a long enough period of time. Depending on the chemical and concentrations, possible health effects include cancer, reproductive or nervous-system disorders and acute toxicity.
Water quality standards are established to assure that the uses of water are protected. The U.S. Environmental Protection Agency (EPA) provides oversight and guidance in the development of water quality standards. Water quality standards are determined based on one or all of the following considerations: beneficial use for the waters, numeric and narrative criteria for supporting each use and an antidegradation statement.
Designated beneficial uses are the desired uses the water quality should support. Numeric criteria establish the minimum physical, chemical, and biological parameters required to support a beneficial use. Narrative water-quality criteria define conditions and attainable goals that must be maintained to support a designated use. Antidegradation statements protect existing uses and prevent water bodies from deteriorating even if their water quality is better than necessary for an existing use.
In 2000, 19% of the streams in the United States were surveyed to determine the water quality conditions of those waters. Of the streams sampled, 53% met the designated water quality use criteria and 8% supported existing beneficial uses but may not in the future unless action is taken. Some form of pollution or habitat degradation impairs the remaining 39% of the assessed streams.
Water monitoring measurements require frequent, preselected and repetitive sampling. However, the use of expensive, time consuming diagnostic methodologies is not appropriate.
Legislation versus cost
Legalization determines what parameters are monitored in relation to issues such as chemical quality of drinking water, waste disposal etc. Once a substance is implicated by legislation, sensors will be required to monitor it. However, species in water can often be determined accurately and cost-effectively by existing laboratory analytical methods. Sensors are only required if it is necessary to monitor the species at the point of discharge, or in the external environment.
In addition, legislators only stipulate continuous monitoring if realistic technologies exist. A very large number of chemical and other quantities are implicated by legislation, but no generic measurement techniques, sensing principles or technologies are available for their determination.
Optical technology on water quality measurement
One of the most obvious places to start, is to replace, simplify and reduce the size of existing optical instruments using current spectrometric and chemical techniques, to make them cheaper, more compact, and remove them from the laboratory, to the test site (Colin and Quevauviller, 1997).
The replacement of existing sensors and monitoring instruments and techniques with optical techniques, depends on the following factors:
- Will they work better and be more reliable and accurate with improved sensitivity, specificity, response time and capability of measuring new parameters?
- Will they offer economical benefits over existing techniques: i.e. are they cheaper?
- Reducing ownership costs; multiparameter sensors, disposable sensors, on-line sensors also reduce cost.
- Situations where sampling and laboratory analysis is too slow and/or costly.
- Colin F. and Quevauviller P. (editors) (1997). In Proceedings of the European Workshop on Standards, Measurements and Testing for the Monitoring of Water Quality: the Contribution of Advanced Technologies, Nancy, France, 29-31 May, ELSEVIER SCIENCE Ltd., UK, ISBN: 008-043340-5 (Paper: Scully P., Optical techniques for water monitoring, p. 15-35).
- Vandas S.J., T.C. Winter and W.A. Battaglin (2002). Water and the environment. American Geological Institute in cooperation with Bureau of Reclamation, National Park Service, U.S. Army Corps of Engineers, USDA Forest Service, U.S. Geological Survey, ISBN: 0-922152-63-2.