Water quality refers to the chemical, physical, and biological characteristics of water based on the standards of its usage. [1] [2] It is most frequently used by reference to a set of standards against which compliance, generally achieved through treatment of the water, can be assessed. The most common standards used to monitor and assess water quality convey the health of ecosystems, safety of human contact, extent of water pollution and condition of drinking water. Water quality has a significant impact on water supply and often determines supply options. [3]
Over time, there has been increasing recognition of the importance of drinking water quality and its impact on public health. This has led to increasing protection and management of water quality. [4]
The understanding of the links between water quality and health continues to grow and highlight new potential health crises: from the chronic impacts of infectious diseases on child development through stunting to new evidence on the harms from known contaminants, such as manganese with growing evidence of neurotoxicity in children. [4] In addition, there are many emerging water quality issues—such as microplastics, perfluorinated compounds, and antimicrobial resistance. [4]
The parameters for water quality are determined by the intended use. Work in the area of water quality tends to be focused on water that is treated for potability, industrial/domestic use, or restoration (of an environment/ecosystem, generally for health of human/aquatic life). [5]
Contaminants that may be in untreated water include microorganisms such as viruses, protozoa and bacteria; inorganic contaminants such as salts and metals; organic chemical contaminants from industrial processes and petroleum use; pesticides and herbicides; and radioactive contaminants. Water quality depends on the local geology and ecosystem, as well as human uses such as sewage dispersion, industrial pollution, use of water bodies as a heat sink, and overuse (which may lower the level of the water).[ citation needed ]
The United States Environmental Protection Agency [6] (EPA) limits the amounts of certain contaminants in tap water provided by US public water systems. The Safe Drinking Water Act authorizes EPA to issue two types of standards:
The U.S. Food and Drug Administration (FDA) regulations establish limits for contaminants in bottled water. [10] Drinking water, including bottled water, may reasonably be expected to contain at least small amounts of some contaminants. The presence of these contaminants does not necessarily indicate that the water poses a health risk.
In urbanized areas around the world, water purification technology is used in municipal water systems to remove contaminants from the source water (surface water or groundwater) before it is distributed to homes, businesses, schools and other recipients. Water drawn directly from a stream, lake, or aquifer and that has no treatment will be of uncertain quality in terms of potability. [3]
The burden of polluted drinking water disproportionally effects under-represented and vulnerable populations. [11] Communities that lack these clean drinking-water services are at risk of contracting water-borne and pollution-related illnesses like Cholera, diarrhea, dysentery, hepatitis A, typhoid, and polio. [12] These communities are often in low-income areas, where human wastewater is discharged into a nearby drainage channel or surface water drain without sufficient treatment, or is used in agricultural irrigation.
Dissolved ions may affect the suitability of water for a range of industrial and domestic purposes. The most familiar of these is probably the presence of calcium (Ca2+) and magnesium (Mg2+) that interfere with the cleaning action of soap, and can form hard sulfate and soft carbonate deposits in water heaters or boilers. [13] Hard water may be softened to remove these ions. The softening process often substitutes sodium cations. [14] For certain populations, hard water may be preferable to soft water because health problems have been associated with calcium deficiencies and with excess sodium. [15] The necessity for additional calcium and magnesium in water depends on the population in question because people generally satisfy their recommended amounts through food. [3] : 99, 115, 377
Environmental water quality, also called ambient water quality, relates to water bodies such as lakes, rivers, and oceans. [16] Water quality standards for surface waters vary significantly due to different environmental conditions, ecosystems, and intended human uses. Toxic substances and high populations of certain microorganisms can present a health hazard [17] for non-drinking purposes such as irrigation, swimming, fishing, rafting, boating, and industrial uses. These conditions may also affect wildlife, which use the water for drinking or as a habitat. According to the EPA, water quality laws generally specify protection of fisheries and recreational use and require, as a minimum, retention of current quality standards. [18] In some locations, desired water quality conditions include high dissolved oxygen concentrations, low chlorophyll-a concentrations, and high water clarity. [19]
There is some desire among the public to return water bodies to pristine, or pre-industrial conditions. [20] Most current environmental laws focus on the designation of particular uses of a water body. In some countries these designations allow for some water contamination as long as the particular type of contamination is not harmful to the designated uses. Given the landscape changes (e.g., land development, urbanization, clearcutting in forested areas) in the watersheds of many freshwater bodies, returning to pristine conditions would be a significant challenge. In these cases, environmental scientists focus on achieving goals for maintaining healthy ecosystems and may concentrate on the protection of populations of endangered species and protecting human health.
The complexity of water quality as a subject is reflected in the many types of measurements of water quality indicators. Some measurements of water quality are most accurately made on-site, because water exists in equilibrium with its surroundings. Measurements commonly made on-site and in direct contact with the water source in question include temperature, pH, dissolved oxygen, conductivity, oxygen reduction potential (ORP), turbidity, and Secchi disk depth.
Sampling of water for physical or chemical testing can be done by several methods, depending on the accuracy needed and the characteristics of the contaminant. Sampling methods include for example simple random sampling, stratified sampling, systematic and grid sampling, adaptive cluster sampling, grab samples, semi-continuous monitoring and continuous, passive sampling, remote surveillance, remote sensing, and biomonitoring. The use of passive samplers greatly reduces the cost and the need of infrastructure on the sampling location.
Many contamination events are sharply restricted in time, most commonly in association with rain events. For this reason "grab" samples are often inadequate for fully quantifying contaminant levels. [21] Scientists gathering this type of data often employ auto-sampler devices that pump increments of water at either time or discharge intervals.
More complex measurements are often made in a laboratory requiring a water sample to be collected, preserved, transported, and analyzed at another location.
The process of water sampling introduces two significant problems:
Sample preservation may partially resolve the second problem. A common procedure is keeping samples cold to slow the rate of chemical reactions and phase change, and analyzing the sample as soon as possible; but this merely minimizes the changes rather than preventing them. [23] : 43–45 A useful procedure for determining influence of sample containers during delay between sample collection and analysis involves preparation for two artificial samples in advance of the sampling event. One sample container is filled with water known from previous analysis to contain no detectable amount of the chemical of interest. This sample, called a "blank", is opened for exposure to the atmosphere when the sample of interest is collected, then resealed and transported to the laboratory with the sample for analysis to determine if sample collection or holding procedures introduced any measurable amount of the chemical of interest. The second artificial sample is collected with the sample of interest, but then "spiked" with a measured additional amount of the chemical of interest at the time of collection. The blank (negative control) and spiked sample (positive control) are carried with the sample of interest and analyzed by the same methods at the same times to determine any changes indicating gains or losses during the elapsed time between collection and analysis. [25]
After events such as earthquakes and tsunamis, there is an immediate response by the aid agencies as relief operations get underway to try and restore basic infrastructure and provide the basic fundamental items that are necessary for survival and subsequent recovery. [26] The threat of disease increases hugely due to the large numbers of people living close together, often in squalid conditions, and without proper sanitation. [27]
After a natural disaster, as far as water quality testing is concerned, there are widespread views on the best course of action to take and a variety of methods can be employed. The key basic water quality parameters that need to be addressed in an emergency are bacteriological indicators of fecal contamination, free chlorine residual, pH, turbidity and possibly conductivity/total dissolved solids. There are many decontamination methods. [28] [29]
After major natural disasters, a considerable length of time might pass before water quality returns to pre-disaster levels. For example, following the 2004 Indian Ocean tsunami the Colombo-based International Water Management Institute (IWMI) monitored the effects of saltwater and concluded that the wells recovered to pre-tsunami drinking water quality one and a half years after the event. [30] IWMI developed protocols for cleaning wells contaminated by saltwater; these were subsequently officially endorsed by the World Health Organization as part of its series of Emergency Guidelines. [31]
The simplest methods of chemical analysis are those measuring chemical elements without respect to their form. Elemental analysis for oxygen, as an example, would indicate a concentration of 890 g/L (grams per litre) of water sample because oxygen (O) has 89% mass of the water molecule (H2O). The method selected to measure dissolved oxygen should differentiate between diatomic oxygen and oxygen combined with other elements. The comparative simplicity of elemental analysis has produced a large amount of sample data and water quality criteria for elements sometimes identified as heavy metals. Water analysis for heavy metals must consider soil particles suspended in the water sample. These suspended soil particles may contain measurable amounts of metal. Although the particles are not dissolved in the water, they may be consumed by people drinking the water. Adding acid to a water sample to prevent loss of dissolved metals onto the sample container may dissolve more metals from suspended soil particles. Filtration of soil particles from the water sample before acid addition, however, may cause loss of dissolved metals onto the filter. [32] The complexities of differentiating similar organic molecules are even more challenging.
Making these complex measurements can be expensive. Because direct measurements of water quality can be expensive, ongoing monitoring programs are typically conducted and results released by government agencies. However, there are local volunteer programs and resources available for some general assessment. [33] Tools available to the general public include on-site test kits, commonly used for home fish tanks, and biological assessment procedures.
Biosensors have the potential for "high sensitivity, selectivity, reliability, simplicity, low-cost and real-time response". [34] For instance, bionanotechnologists reported the development of ROSALIND 2.0, that can detect levels of diverse water pollutants. [35] [36]
Although water quality is usually sampled and analyzed at laboratories, since the late 20th century there has been increasing public interest in the quality of drinking water provided by municipal systems. Many water utilities have developed systems to collect real-time data about source water quality. In the early 21st century, a variety of sensors and remote monitoring systems have been deployed for measuring water pH, turbidity, dissolved oxygen and other parameters. [37] Some remote sensing systems have also been developed for monitoring ambient water quality in riverine, estuarine and coastal water bodies. [38] [39]
The following is a list of indicators often measured by situational category:
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Biological monitoring metrics have been developed in many places, and one widely used family of measurements for freshwater is the presence and abundance of members of the insect orders Ephemeroptera, Plecoptera and Trichoptera (EPT) (of benthic macroinvertebrates whose common names are, respectively, mayfly, stonefly and caddisfly). EPT indexes will naturally vary from region to region, but generally, within a region, the greater the number of taxa from these orders, the better the water quality. Organisations in the United States, such as EPA. offer guidance on developing a monitoring program and identifying members of these and other aquatic insect orders. Many US wastewater dischargers (e.g., factories, power plants, refineries, mines, municipal sewage treatment plants) are required to conduct periodic whole effluent toxicity (WET) tests. [40] [41]
Individuals interested in monitoring water quality who cannot afford or manage lab scale analysis can also use biological indicators to get a general reading of water quality. One example is the IOWATER volunteer water monitoring program of Iowa, which includes an EPT indicator key. [42]
Bivalve molluscs are largely used as bioindicators to monitor the health of aquatic environments in both fresh water and the marine environments. Their population status or structure, physiology, behaviour or the level of contamination with elements or compounds can indicate the state of contamination status of the ecosystem. They are particularly useful since they are sessile so that they are representative of the environment where they are sampled or placed. A typical project is the U.S. Mussel Watch Programme, [43] but today they are used worldwide.
The Southern African Scoring System (SASS) method is a biological water quality monitoring system based on the presence of benthic macroinvertebrates (EPT). The SASS aquatic biomonitoring tool has been refined over the past 30 years and is now on the fifth version (SASS5) which has been specifically modified in accordance with international standards, namely the ISO/IEC 17025 protocol. [44] The SASS5 method is used by the South African Department of Water Affairs as a standard method for River Health Assessment, which feeds the national River Health Programme and the national Rivers Database.
Weather and its related shocks can affect water quality in several ways. These depend on the local climate and context. [45] Shocks that are linked to weather include water shortages, heavy rain and temperature extremes. They can damage water infrastructure through erosion under heavy rainfall and floods, cause loss of water sources in droughts, and make water quality deteriorate. [45]
Climate change can reduce lower water quality in several ways: [46] : 582
In the setting of standards, agencies make political and technical/scientific decisions based on how the water will be used. [55] In the case of natural water bodies, agencies also make some reasonable estimate of pristine conditions. Natural water bodies will vary in response to a region's environmental conditions, whereby water composition is influenced by the surrounding geological features, sediments, and rock types, topography, hydrology, and climate. [56] Environmental scientists and aqueous geochemists work to interpret the parameters and environmental conditions that impact the water quality of a region, which in turn helps to identify the sources and fates of contaminants. Environmental lawyers and policymakers work to define legislation with the intention that water is maintained at an appropriate quality for its identified use.
Another general perception of water quality is that of a simple property that tells whether water is polluted or not. In fact, water quality is a complex subject, in part because water is a complex medium intrinsically tied to the ecology, geology, and anthropogenic activities of a region. Industrial and commercial activities (e.g. manufacturing, mining, construction, transport) are a major cause of water pollution as are runoff from agricultural areas, urban runoff and discharge of treated and untreated sewage.[ citation needed ]
The water policy of the European Union is primarily codified in three directives:
Water quality guidelines for South Africa are grouped according to potential user types (e.g. domestic, industrial) in the 1996 Water Quality Guidelines. [59] Drinking water quality is subject to the South African National Standard (SANS) 241 Drinking Water Specification. [60]
In England and Wales acceptable levels for drinking water supply are listed in the "Water Supply (Water Quality) Regulations 2000." [61]
In the United States, Water Quality Standards are defined by state agencies for various water bodies, guided by the desired uses for the water body (e.g., fish habitat, drinking water supply, recreational use). [62] The Clean Water Act (CWA) requires each governing jurisdiction (states, territories, and covered tribal entities) to submit a set of biennial reports on the quality of water in their area. These reports are known as the 303(d) and 305(b) reports, named for their respective CWA provisions, and are submitted to, and approved by, EPA. [63] These reports are completed by the governing jurisdiction, typically a state environmental agency. EPA recommends that each state submit a single "Integrated Report" comprising its list of impaired waters and the status of all water bodies in the state. [64] The National Water Quality Inventory Report to Congress is a general report on water quality, providing overall information about the number of miles of streams and rivers and their aggregate condition. [65] The CWA requires states to adopt standards for each of the possible designated uses that they assign to their waters. Should evidence suggest or document that a stream, river or lake has failed to meet the water quality criteria for one or more of its designated uses, it is placed on a list of impaired waters. Once a state has placed a water body on this list, it must develop a management plan establishing Total Maximum Daily Loads (TMDLs) for the pollutant(s) impairing the use of the water. These TMDLs establish the reductions needed to fully support the designated uses. [66]
Drinking water standards, which are applicable to public water systems, are issued by EPA under the Safe Drinking Water Act. [8]
Drinking water or potable water is water that is safe for ingestion, either when drunk directly in liquid form or consumed indirectly through food preparation. It is often supplied through taps, in which case it is also called tap water. Typically in developed countries, tap water meets drinking water quality standards, even though only a small proportion is actually consumed or used in food preparation. Other typical uses for tap water include washing, toilets, and irrigation. Greywater may also be used for toilets or irrigation. Its use for irrigation however may be associated with risks.
Turbidity is the cloudiness or haziness of a fluid caused by large numbers of individual particles that are generally invisible to the naked eye, similar to smoke in air. The measurement of turbidity is a key test of both water clarity and water quality.
Water pollution is the contamination of water bodies, with a negative impact on their uses. It is usually a result of human activities. Water bodies include lakes, rivers, oceans, aquifers, reservoirs and groundwater. Water pollution results when contaminants mix with these water bodies. Contaminants can come from one of four main sources. These are sewage discharges, industrial activities, agricultural activities, and urban runoff including stormwater. Water pollution may affect either surface water or groundwater. This form of pollution can lead to many problems. One is the degradation of aquatic ecosystems. Another is spreading water-borne diseases when people use polluted water for drinking or irrigation. Water pollution also reduces the ecosystem services such as drinking water provided by the water resource.
Environmental remediation is the cleanup of hazardous substances dealing with the removal, treatment and containment of pollution or contaminants from environmental media such as soil, groundwater, sediment. Remediation may be required by regulations before development of land revitalization projects. Developers who agree to voluntary cleanup may be offered incentives under state or municipal programs like New York State's Brownfield Cleanup Program. If remediation is done by removal the waste materials are simply transported off-site for disposal at another location. The waste material can also be contained by physical barriers like slurry walls. The use of slurry walls is well-established in the construction industry. The application of (low) pressure grouting, used to mitigate soil liquefaction risks in San Francisco and other earthquake zones, has achieved mixed results in field tests to create barriers, and site-specific results depend upon many variable conditions that can greatly impact outcomes.
Biochemical oxygen demand is an analytical parameter representing the amount of dissolved oxygen (DO) consumed by aerobic bacteria growing on the organic material present in a water sample at a specific temperature over a specific time period. The BOD value is most commonly expressed in milligrams of oxygen consumed per liter of sample during 5 days of incubation at 20 °C and is often used as a surrogate of the degree of organic water pollution.
A perchlorate is a chemical compound containing the perchlorate ion, ClO−4, the conjugate base of perchloric acid. As counterions, there can be metal cations, quaternary ammonium cations or other ions, for example, nitronium cation.
Environmental chemistry is the scientific study of the chemical and biochemical phenomena that occur in natural places. It should not be confused with green chemistry, which seeks to reduce potential pollution at its source. It can be defined as the study of the sources, reactions, transport, effects, and fates of chemical species in the air, soil, and water environments; and the effect of human activity and biological activity on these. Environmental chemistry is an interdisciplinary science that includes atmospheric, aquatic and soil chemistry, as well as heavily relying on analytical chemistry and being related to environmental and other areas of science.
Total organic carbon (TOC) is an analytical parameter representing the concentration of organic carbon in a sample. TOC determinations are made in a variety of application areas. For example, TOC may be used as a non-specific indicator of water quality, or TOC of source rock may be used as one factor in evaluating a petroleum play. For marine surface sediments average TOC content is 0.5% in the deep ocean, and 2% along the eastern margins.
Hexavalent chromium (chromium(VI), Cr(VI), chromium 6) is any chemical compound that contains the element in the +6 oxidation state (thus hexavalent). It has been identified as carcinogenic, which is of concern since approximately 136,000 tonnes (150,000 tons) of hexavalent chromium were produced in 1985. Hexavalent chromium compounds can be carcinogens (IARC Group 1), especially if airborne and inhaled where they can cause lung cancer.
The Safe Drinking Water Act (SDWA) is the primary federal law in the United States intended to ensure safe drinking water for the public. Pursuant to the act, the Environmental Protection Agency (EPA) is required to set standards for drinking water quality and oversee all states, localities, and water suppliers that implement the standards.
Total dissolved solids (TDS) is a measure of the dissolved combined content of all inorganic and organic substances present in a liquid in molecular, ionized, or micro-granular suspended form. TDS are often measured in parts per million (ppm). TDS in water can be measured using a digital meter.
Water testing is a broad description for various procedures used to analyze water quality. Millions of water quality tests are carried out daily to fulfill regulatory requirements and to maintain safety.
Drinking water quality in the United States is generally safe. In 2016, over 90 percent of the nation's community water systems were in compliance with all published U.S. Environmental Protection Agency standards. Over 286 million Americans get their tap water from a community water system. Eight percent of the community water systems—large municipal water systems—provide water to 82 percent of the US population. The Safe Drinking Water Act requires the US EPA to set standards for drinking water quality in public water systems. Enforcement of the standards is mostly carried out by state health agencies. States may set standards that are more stringent than the federal standards.
Environmental monitoring is the processes and activities that are done to characterize and describe the state of the environment. It is used in the preparation of environmental impact assessments, and in many circumstances in which human activities may cause harmful effects on the natural environment. Monitoring strategies and programs are generally designed to establish the current status of an environment or to establish a baseline and trends in environmental parameters. The results of monitoring are usually reviewed, analyzed statistically, and published. A monitoring program is designed around the intended use of the data before monitoring starts.
Water chemistry analyses are carried out to identify and quantify the chemical components and properties of water samples. The type and sensitivity of the analysis depends on the purpose of the analysis and the anticipated use of the water. Chemical water analysis is carried out on water used in industrial processes, on waste-water stream, on rivers and stream, on rainfall and on the sea. In all cases the results of the analysis provides information that can be used to make decisions or to provide re-assurance that conditions are as expected. The analytical parameters selected are chosen to be appropriate for the decision-making process or to establish acceptable normality. Water chemistry analysis is often the groundwork of studies of water quality, pollution, hydrology and geothermal waters. Analytical methods routinely used can detect and measure all the natural elements and their inorganic compounds and a very wide range of organic chemical species using methods such as gas chromatography and mass spectrometry. In water treatment plants producing drinking water and in some industrial processes using products with distinctive taste and odors, specialized organoleptic methods may be used to detect smells at very low concentrations.
Air sparging, also known as in situ air stripping and in situ volatilization is an in situ remediation technique, used for the treatment of saturated soils and groundwater contaminated by volatile organic compounds (VOCs) like petroleum hydrocarbons, a widespread problem for the ground water and soil health. Vapor extraction has become a very successful and practical method of VOC remediation. In saturated zone remediation, air sparging refers to the injection a hydrocarbon-free gaseous medium into the ground where contamination has been found. When it comes to situ air sparging it became an intricate phase process that was proven to be successful in Europe since the 1980s. Currently, there have been further developments into bettering the engineering design and process of air sparging.
Groundwater pollution occurs when pollutants are released to the ground and make their way into groundwater. This type of water pollution can also occur naturally due to the presence of a minor and unwanted constituent, contaminant, or impurity in the groundwater, in which case it is more likely referred to as contamination rather than pollution. Groundwater pollution can occur from on-site sanitation systems, landfill leachate, effluent from wastewater treatment plants, leaking sewers, petrol filling stations, hydraulic fracturing (fracking) or from over application of fertilizers in agriculture. Pollution can also occur from naturally occurring contaminants, such as arsenic or fluoride. Using polluted groundwater causes hazards to public health through poisoning or the spread of disease.
Headspace gas chromatography uses headspace gas—from the top or "head" of a sealed container containing a liquid or solid brought to equilibrium—injected directly onto a gas chromatographic column for separation and analysis. In this process, only the most volatile substances make it to the column. The technique is commonly applied to the analysis of polymers, food and beverages, blood alcohol levels, environmental variables, cosmetics, and pharmaceutical ingredients.
Contaminants of emerging concern (CECs) is a term used by water quality professionals to describe pollutants that have been detected in environmental monitoring samples, that may cause ecological or human health impacts, and typically are not regulated under current environmental laws. Sources of these pollutants include agriculture, urban runoff and ordinary household products and pharmaceuticals that are disposed to sewage treatment plants and subsequently discharged to surface waters.
The Wellhead Protection Program in the 1986 amendments to the Safe Drinking Water Act requires states to protect underground sources of drinking water from contaminants that may adversely affect human health. Over half of the U.S. population relies on groundwater for drinking water However, residential, municipal, commercial, industrial, and agricultural activities can all contaminate groundwater. In the event of contamination, a community's drinking water supply can develop poor quality or be lost altogether. Groundwater contamination occurs from products such as oil, chemicals, gasoline, or other toxic substances to infiltrate groundwater. These products can travel through soil and seep into the groundwater; this process can occur through landfills, septic tanks, mining sites, fertilization, etc. Groundwater contamination might not be detected for a long period of time and health problems can occur from drinking contaminated water. Cleanup of a contaminated underground source of drinking water may be impossible or so difficult it costs thousands or millions of dollars. The U.S. Congress requiring Wellhead Protection Programs by 42 U.S.C. § 300h–7 in the Safe Drinking Water Act applied the concept that it is better to prevent groundwater contamination than try to remediate it. U.S. Congress by 42 U.S.C. § 300h–7 requires identification of the areas that need implementation of control measures in order to protect public water supply wells from contamination as "wellhead protection areas". Communities can use the police power established by the Tenth Amendment to the U.S. Constitution to enforce zoning and subdivision regulations to protect drinking water sources. Thereby communities can direct development away from areas that would pose a threat to drinking water sources.
Plastic is the most common type of marine debris found in oceans, and it is the most widespread problem affecting the marine environment. It also threatens ocean health, food safety and quality, human health, and coastal tourism, and it contributes to climate change
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