Water quality is the physical, chemical andbiological characteristics of water. It is ameasure of the condition of water relative tothe requirements of one or more bioticspecies and or to any human need orpurpose. It is most frequently used byreference to a set of standards against whichcompliance can be assessed. The mostcommon standards used to assess waterquality relate to health of ecosystems, safetyof human contact and drinking water.
In the setting of standards, agencies makepolitical and technical/scientific decisionsabout how the water will be used. In the caseof natural water bodies, they also make somereasonable estimate of pristine conditions.Different uses raise different concerns andtherefore different standards are considered.Natural water bodies will vary in response toenvironmental conditions.
Environmental scientists work to understandhow these systems function, which in turnhelps to identify the sources and fates ofcontaminants. Environmental lawyers andpolicymakers work to define legislation withthe intention that water is maintained at anappropriate quality for its identified use.
The vast majority of surface water on the planetis neither potable nor toxic. This remains trueeven if seawater in the oceans (which is too saltyto drink) is not counted. Another generalperception of water quality is that of a simpleproperty that tells whether water is polluted ornot. In fact, water quality is a complex subject, inpart because water is a complex mediumintrinsically tied to the ecology of the Earth.Industrial and commercial activities (e.g.manufacturing, mining, construction, transport)are a major cause of water pollution as are runofffrom agricultural areas, urban runoff anddischarge of treated and untreated sewage.
The parameters for water quality aredetermined by the intended use. Work in thearea of water quality tends to be focused onwater that is treated for human consumption,industrial use, or in the environment.
Contaminants that may be in untreated waterinclude microorganisms such as viruses andbacteria; inorganic contaminants such as saltsand metals; organic chemical contaminants fromindustrial processes and petroleum use;pesticides and herbicides; and radioactivecontaminants. Water quality depends on the localgeology and ecosystem, as well as human usessuch as sewage dispersion, industrial pollution,use of water bodies as a heat sink, and overuse(which may lower the level of the water).
The United States Environmental Protection Agency (EPA)limits the amounts of certain contaminants in tap waterprovided by US public water systems. The Safe Drinking WaterAct authorizes EPA to issue two types of standards: primarystandards regulate substances that potentially affect humanhealth, and secondary standards prescribe aesthetic qualities,those that affect taste, odor, or appearance. The U.S. Foodand Drug Administration (FDA) regulations establish limits forcontaminants in bottled water that must provide the sameprotection for public health. Drinking water, including bottledwater, may reasonably be expected to contain at least smallamounts of some contaminants. The presence of thesecontaminants does not necessarily indicate that the waterposes a health risk.
Some people use water purificationtechnology to remove contaminantsfrom the municipal water supply theyget in their homes, or from localpumps or bodies of water. Waterdrawn directly from a stream, lake,or aquifer and has no treatment willbe of uncertain quality
Dissolved minerals may affect suitability of water fora range of industrial and domestic purposes. Themost familiar of these is probably the presence ofions of calcium and magnesium which interfere withthe cleaning action of soap, and can form hardsulfate and soft carbonate deposits in water heatersor boilers. Hard water may be softened to removethese ions. The softening process often substitutessodium cations. Hard water may be preferable to softwater for human consumption, since health problemshave been associated with excess sodium and withcalcium and magnesium deficiencies. Softening maysacrifice nutrition for cleaning effectiveness.
Environmental water quality, also calledambient water quality, relates to water bodiessuch as lakes, rivers, and oceans. Waterquality standards for surface waters varysignificantly due to different environmentalconditions, ecosystems, and intended humanuses. Toxic substances and high populationsof certain microorganisms can present ahealth hazard for non-drinking purposessuch as irrigation, swimming, fishing, rafting,boating, and industrial uses.
These conditions may also affect wildlife,which use the water for drinking or as ahabitat. Modern water quality laws generallyspecify protection of fisheries andrecreational use and require, as a minimum,retention of current quality standards.
There is some desire among the public toreturn water bodies to pristine, or pre-industrial conditions. Most currentenvironmental laws focus on the designationof particular uses of a water body. In somecountries these designations allow for somewater contamination as long as the particulartype of contamination is not harmful to thedesignated uses.
Given the landscape changes (e.g., landdevelopment, urbanization, clearcutting inforested areas) in the watersheds of manyfreshwater bodies, returning to pristineconditions would be a significant challenge.In these cases, environmental scientists focuson achieving goals for maintaining healthyecosystems and may concentrate on theprotection of populations of endangeredspecies and protecting human health.
The complexity of water quality as a subject isreflected in the many types of measurements ofwater quality indicators. The most accuratemeasurements of water quality are made on-site,because water exists in equilibrium with itssurroundings. Measurements commonly madeon-site and in direct contact with the watersource in question include temperature, pH,dissolved oxygen, conductivity, oxygen reductionpotential (ORP), turbidity, and Secchi disk depth.
An automated sampling station installedalong the East Branch Milwaukee River, NewFane, Wisconsin. The cover of the 24-bottleautosampler (center) is partially raised,showing the sample bottles inside. Theautosampler was programmed to collectsamples at time intervals, or proportionate toflow over a specified period. The data logger(white cabinet) recorded temperature, specificconductance, and dissolved oxygen levels.
More complex measurements are often made ina laboratory requiring a water sample to becollected, preserved, transported, and analyzedat another location. The process of watersampling introduces two significant problems.The first problem is the extent to which thesample may be representative of the watersource of interest. Many water sources vary withtime and with location. The measurement ofinterest may vary seasonally or from day to nightor in response to some activity of man or naturalpopulations of aquatic plants and animals.
The measurement of interest may vary withdistances from the water boundary with overlyingatmosphere and underlying or confining soil. Thesampler must determine if a single time andlocation meets the needs of the investigation, orif the water use of interest can be satisfactorilyassessed by averaged values with time and/orlocation, or if critical maxima and minima requireindividual measurements over a range of times,locations and/or events. The sample collectionprocedure must assure correct weighting ofindividual sampling times and locations whereaveraging is appropriate.
Where critical maximum or minimum valuesexist, statistical methods must be applied toobserved variation to determine an adequatenumber of samples to assess probability ofexceeding those critical values.
The second problem occurs as the sample isremoved from the water source and begins toestablish chemical equilibrium with its newsurroundings - the sample container. Samplecontainers must be made of materials withminimal reactivity with substances to bemeasured; and pre-cleaning of samplecontainers is important. The water sample maydissolve part of the sample container and anyresidue on that container, or chemicals dissolvedin the water sample may sorb onto the samplecontainer and remain there when the water ispoured out for analysis.
Similar physical and chemical interactions maytake place with any pumps, piping, orintermediate devices used to transfer the watersample into the sample container. Watercollected from depths below the surface willnormally be held at the reduced pressure of theatmosphere; so gas dissolved in the water mayescape into unfilled space at the top of thecontainer. Atmospheric gas present in that airspace may also dissolve into the water sample.Other chemical reaction equilibria may change ifthe water sample changes temperature.
Finely divided solid particles formerly suspendedby water turbulence may settle to the bottom ofthe sample container, or a solid phase may formfrom biological growth or chemical precipitation.Microorganisms within the water sample maybiochemically alter concentrations of oxygen,carbon dioxide, and organic compounds.Changing carbon dioxide concentrations mayalter pH and change solubility of chemicals ofinterest. These problems are of special concernduring measurement of chemicals assumed to besignificant at very low concentrations.
Filtering a manually collected water sample("grab sample") for analysis
Sample preservation may partially resolve thesecond problem. A common procedure iskeeping samples cold to slow the rate ofchemical reactions and phase change, andanalyzing the sample as soon as possible; butthis merely minimizes the changes ratherthan preventing them. A useful procedure fordetermining influence of sample containersduring delay between sample collection andanalysis involves preparation for two artificialsamples in advance of the sampling event.
One sample container is filled with waterknown from previous analysis to contain nodetectable amount of the chemical ofinterest. This blank sample is opened forexposure to the atmosphere when the sampleof interest is collected, then resealed andtransported to the laboratory with the samplefor analysis to determine if sample holdingprocedures introduced any measurableamount of the chemical of interest.
The second artificial sample is collected withthe sample of interest, but then spiked with ameasured additional amount of the chemicalof interest at the time of collection. The blankand spiked samples are carried with thesample of interest and analyzed by the samemethods at the same times to determine anychanges indicating gains or losses during theelapsed time between collection and analysis.
Inevitably after events such as earthquakes andtsunamis, there is an immediate response by theaid agencies as relief operations get underway totry and restore basic infrastructure and providethe basic fundamental items that are necessaryfor survival and subsequent recovery. Access toclean drinking water and adequate sanitation is apriority at times like this. The threat of diseaseincreases hugely due to the large numbers ofpeople living close together, often in squalidconditions, and without proper sanitation.
After a natural disaster, as far as water qualitytesting is concerned there are widespread viewson the best course of action to take and a varietyof methods can be employed. The key basicwater quality parameters that need to beaddressed in an emergency are bacteriologicalindicators of fecal contamination, free chlorineresidual, pH, turbidity and possiblyconductivity/total dissolved solids. There are anumber of portable water test kits on the marketwidely used by aid and relief agencies forcarrying out such testing.
After major natural disasters, a considerablelength of time might pass before water qualityreturns to pre-disaster levels. For example,following the 2004 Indian Ocean Tsunami theColombo-based International Water ManagementInstitute monitored the effects of saltwater andconcluded that the wells recovered to pre-tsunami drinking water quality one and a halfyears after the event. IWMI developed protocolsfor cleaning wells contaminated by saltwater;these were subsequently officially endorsed bythe World Health Organization as part of itsseries of Emergency Guidelines.
A gas chromatograph-mass spectrometer measures pesticides andother organic polluants
The simplest methods of chemical analysis arethose measuring chemical elements withoutrespect to their form. Elemental analysis fordissolved oxygen, as an example, would indicatea concentration of 890,000 milligrams per litre(mg/L) of water sample because water is made ofoxygen. The method selected to measuredissolved oxygen should differentiate betweendiatomic oxygen and oxygen combined withother elements. The comparative simplicity ofelemental analysis has produced a large amountof sample data and water quality criteria forelements sometimes identified as heavy metals.
Water analysis for heavy metals must considersoil particles suspended in the water sample.These suspended soil particles may containmeasurable amounts of metal. Although theparticles are not dissolved in the water, they maybe consumed by people drinking the water.Adding acid to a water sample to prevent loss ofdissolved metals onto the sample container maydissolve more metals from suspended soilparticles. Filtration of soil particles from thewater sample before acid addition, however, maycause loss of dissolved metals onto the filter.Thecomplexities of differentiating similar organicmolecules are even more challenging.
Making these complexmeasurements can be expensive.Because direct measurements ofwater quality can be expensive,ongoing monitoring programs aretypically conducted by governmentagencies. However, there are localvolunteer programs and resourcesavailable for some generalassessment. Tools available to thegeneral public include on-site testkits, commonly used for home fishtanks, and biological assessmentprocedures.
An electrical conductivity meter is used tomeasure total dissolved solids
AlkalinityColor of waterpHTaste and odor (geosmin, 2- Methylisoborneol(MIB), etc.)Dissolved metals and salts (sodium, chloride, potassium, calcium, manganese, magnesium)Microorganisms such as fecal coliform bacteria (Escherichia coli), Cryptosporidium, and Giardia lamblia
pH Temperature Total suspended solids (TSS) Turbidity Total dissolved solids (TDS)
Biological monitoring metrics have beendeveloped in many places, and one widely usedmeasure is the presence and abundance ofmembers of the insect orders Ephemeroptera,Plecoptera and Trichoptera. (Common names are,respectively, Mayfly, Stonefly and Caddisfly.) EPTindexes will naturally vary from region to region,but generally, within a region, the greater thenumber of taxa from these orders, the better thewater quality. EPA and other organizations in theUnited States offer guidance on developing amonitoring program and identifying members ofthese and other aquatic insect orders.
Individuals interested in monitoring waterquality who cannot afford or manage labscale analysis can also use biologicalindicators to get a general reading of waterquality. One example is the IOWATERvolunteer water monitoring program, whichincludes a benthic macroinvertebrateindicator key.
The Southern African Scoring System (SASS)method is a biological water quality monitoringsystem based on the presence of benthicmacroinvertebrates. The SASS aquaticbiomonitoring tool has been refined over thepast 30 years and is now on the fifth version(SASS5) which has been specifically modified inaccordance with international standards, namelythe ISO/IEC 17025 protocol. The SASS5 methodis used by the South African Department of WaterAffairs as a standard method for River HealthAssessment, which feeds the national RiverHealth Programme and the national RiversDatabase.
The water policy of the European Union is primarily codified in three directives: Directive on Urban Waste Water Treatment (91/271/EEC) of 21 May 1991 concerning discharges of municipal and some industrial wastewaters; The Drinking Water Directive (98/83/EC) of 3 November 1998 concerning potable water quality; Water Framework Directive (2000/60/EC) of 23 October 2000 concerning water resources management.
In England and Wales acceptable levels for drinking water supply are listed in the "Water Supply (Water Quality) Regulations 2000."
In the United States, Water Quality Standards are created by state agencies for different types of water bodies and water body locations per desired uses. 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), 305(b) and 314 reports, named for their respective CWA provisions, and are submitted to, and approved by, EPA. These reports are completed by the governing jurisdiction, typically a state environmental agency, and are available on the web.
In coming years it is expected that the governing jurisdictions will submit all three reports as a single document, called the "Integrated Report." The 305(b) report (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. The 314 report has provided similar information for lakes. The CWA requires states to adopt water quality 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 the 303(d) list of impaired waters. Once a state has placed a water body on the 303(d) list, it must develop a management plan establishing Total Maximum Daily Loads for the pollutant(s) impairing the use of the water. These TMDLs establish the reductions needed to fully support the designated uses.
Water quality regulated by ISO is covered in the section of ICS 13.060, ranging from water sampling, drinking water, industrial class water, sewage water, and examination of water for chemical, physical or biological properties. ICS 91.140.60 covers the standards of water supply system