http://en.wikipedia.org/wiki/Water_quality
From Wikipedia, the free encyclopedia
A rosette
sampler is used to collect samples in deep water, such as theGreat Lakes or oceans, for water quality
testing.
Water quality refers to the chemical, physical and biological characteristics of water.[1] It is a measure of the
condition of water relative to the requirements of one or more biotic species
and or to any human need or purpose.[2] It is most frequently used by
reference to a set of standards against which compliance can be assessed. The
most common standards used to assess water quality relate to health of ecosystems, safety of human contact and drinking water.
Contents
In the setting of standards,
agencies make political and technical/scientific decisions about how the water
will be used.[3] In the case of natural water bodies, they also make some reasonable
estimate of pristine conditions. Different uses raise different concerns and
therefore different standards are considered. Natural water bodies will vary in
response to environmental conditions. Environmental
scientists work to understand how these systems function, 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.
The vast majority of surface water on the planet is neither potable nor toxic. This remains true when seawater in the oceans (which is too
salty to drink) is not counted. 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 of the Earth. 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.
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 human consumption, industrial use, or
in the environment.
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).
The United
States Environmental Protection Agency (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: primary
standards regulate substances that potentially affect human health,
and secondary standards prescribe aesthetic qualities, those
that affect taste, odor, or appearance. The U.S. Food and Drug
Administration (FDA) regulations establish limits for
contaminants in bottled waterthat
must provide the same protection for public health. 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 orgroundwater) before it
is distributed to homes, businesses, schools and other users. Water drawn
directly from a stream, lake, or aquifer and that has no treatment will be
of uncertain quality.
Dissolved minerals may affect
suitability of water for a range of industrial and domestic purposes. The most
familiar of these is probably the presence of ions of calcium andmagnesium which interfere with the
cleaning action of soap, and can form hard sulfate and soft carbonate deposits in water heaters or boilers.[4] Hard water may be softened to
remove these ions. The softening process often substitutes sodium cations.[5] Hard water may be preferable to
soft water for human consumption, since health problems have been associated
with excess sodium and with calcium and magnesium deficiencies. Softening decreases
nutrition and may increase cleaning effectiveness.[6]
Urban runoff discharging to coastal
waters
Environmental water quality, also
called ambient water quality, relates to water bodies such as
lakes, rivers, and oceans. 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 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. Modern
water quality laws generally specify protection of fisheries and recreational
use and require, as a minimum, retention of current quality standards.
Satirical
cartoon by William Heath,
showing a woman observing monsters in a drop of London water (at the time of
the Commission on the London Water Supply report, 1828)
There is some desire among the
public to return water bodies to pristine, or pre-industrial conditions. 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.
See also: water chemistry
analysis and analytical chemistry
The complexity of water quality
as a subject is reflected in the many types of measurements of water quality
indicators. The most accurate measurements of water quality are 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.
An automated
sampling station installed along the East BranchMilwaukee River, New Fane, Wisconsin.
The cover of the 24-bottle autosampler (center) is partially raised, showing
the sample bottles inside. The autosampler was programmed to collect samples at
time intervals, or proportionate to flow over a specified period. The data
logger (white cabinet) recorded temperature, specific conductance, and
dissolved oxygen levels.
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.
The first problem is the extent to which the sample may be representative of
the water source of interest. Many water sources vary with time and with
location. The measurement of interest may vary seasonally or from day to night
or in response to some activity of man or natural populations of aquatic plants
and animals.[7] The measurement of interest may
vary with distances from the water boundary with overlyingatmosphere and
underlying or confining soil. The sampler must
determine if a single time and location meets the needs of the investigation,
or if the water use of interest can be satisfactorily assessed by averaged values with time and/or
location, or if criticalmaxima and minima require
individual measurements over a range of times, locations and/or events. The
sample collection procedure must assure correct weighting of individual
sampling times and locations where averaging is appropriate.[8]:39–40 Where critical maximum or
minimum values exist, statistical methods must
be applied to observed variation to determine an adequate number of samples to
assess probability of
exceeding those critical values.[9]
The second problem occurs as the
sample is removed from the water source and begins to establish chemical equilibrium with
its new surroundings - the sample container. Sample containers must be made of
materials with minimal reactivity with substances to be measured; and
pre-cleaning of sample containers is important. The water sample may dissolve
part of the sample container and any residue on that container, or chemicals
dissolved in the water sample may sorb onto the sample container and remain
there when the water is poured out for analysis.[8]:4 Similar physical and chemical
interactions may take place with any pumps, piping, or intermediate devices
used to transfer the water sample into the sample container. Water collected
from depths below the surface will normally be held at the reduced pressure of the atmosphere; so gas dissolved in the water may escape into
unfilled space at the top of the container. Atmospheric gas present in that air
space may also dissolve into the water sample. Other chemical reaction
equilibria may change if the water sample changes temperature. Finely divided
solid particles formerly suspended by water turbulence may settle
to the bottom of the sample container, or a solid phase may form from
biological growth or chemical
precipitation. Microorganisms within the water sample
may biochemically alter concentrations of oxygen, carbon dioxide, and organic compounds. Changing carbon dioxide
concentrations may alter pH and change solubility
of chemicals of interest. These problems are of special concern during
measurement of chemicals assumed to be significant at very low concentrations.[10]
Filtering a
manually collected water sample (grab sample)
for analysis
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.[8]: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 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 and spiked samples
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.[11]
Inevitably 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. Access to clean drinking water and adequate sanitation is
a priority at times like this. The threat of disease increases hugely due to
the large numbers of people living close together, often in squalid conditions,
and without proper sanitation.
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 a number of portable
water test kits on the market widely used by aid and relief agencies for
carrying out such testing.
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.[12] 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.[13]
A gas
chromatograph-
mass spectrometer measurespesticides and other organic pollutants
mass spectrometer measurespesticides and other organic pollutants
The simplest methods of chemical
analysis are those measuring chemical elements without respect to
their form. Elemental analysis for dissolved oxygen, as an example, would
indicate a concentration of 890,000 milligrams per litre (mg/L) of water sample
because water is made of oxygen. 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.[14] 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 by government
agencies. However, there are local volunteer programs and resources available
for some general assessment. Tools available to the general public include
on-site test kits, commonly used for home fish tanks, and biological assessment
procedures.
An electrical
conductivity meter is used to measure total dissolved
solids
The following is a list of
indicators often measured by situational category:
·
pH
·
Taste and odor (geosmin, 2-Methylisoborneol (MIB),
etc.)
·
Microorganisms such as fecal coliform bacteria (Escherichia
coli), Cryptosporidium,
and Giardia lamblia; see Bacteriological
water analysis
·
Dissolved organics: colored
dissolved organic matter (CDOM), dissolved organic
carbon (DOC)
·
Radon
·
Hormone analogs
See also: Environmental
indicator, Wastewater
quality indicators, and Salinity
·
Water Temperature
·
Total suspended
solids (TSS)
·
Transparency or Turbidity
|
·
Total dissolved
solids (TDS)
·
Odour of water
·
Taste of water
|
·
pH
·
Biochemical
oxygen demand (BOD)
·
Chemical oxygen
demand (COD)
·
Dissolved oxygen (DO)
·
Total hardness (TH)
|
·
Nitrate
|
See also: Biological integrity and Index of
biological integrity
|
·
Mollusca
|
Biological monitoring metrics
have been developed in many places, and one widely used measure is the presence
and abundance of members of the insect ordersEphemeroptera, Plecoptera and Trichoptera. (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.[15][16]
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, which includes a benthic macroinvertebrate indicator key.[17]
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 Mussel Watch Programme,[18] 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. 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.[19] 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.
·
World Health
Organisation (WHO) guideline for Drinking Water Standards.[20]
·
Indian
Council of Medical Research (ICMR) Standards for Drinking
Water.[21]
Water quality regulated by the International
Organization for Standardization (ISO) is covered in the
section of ICS 13.060,[22] 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 systems.[23]
Further information: Water supply and sanitation in the European Union
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."[24]
Further information: Water
supply and sanitation in South Africa
Water quality guidelines for
South Africa are grouped according to potential user types (e.g. domestic,
industrial) in the 1996 Water Quality Guidelines.[25] Drinking water quality is
subject to the South African National Standard (SANS) 241 Drinking Water
Specification.[26]
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.[27] 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.[28] 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.[29] The 314 report has provided
similar information for lakes.[30] 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.[31]
|
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1. ^ Diersing, Nancy (2009). "Water Quality: Frequently Asked Questions." Florida
Brooks National Marine Sanctuary, Key West, FL.
2. ^ Johnson, D.L., S.H.
Ambrose, T.J. Bassett, M.L. Bowen, D.E. Crummey, J.S. Isaacson, D.N. Johnson,
P. Lamb, M. Saul, and A.E. Winter-Nelson (1997). "Meanings of
environmental terms." Journal of Environmental Quality. 26:
581-589.doi:10.2134/jeq1997.00472425002600030002x
3. ^ United States
Environmental Protection Agency (EPA). Washington, DC. "Water Quality Standards Review and Revision." 2006.
5. ^ Linsley, Ray K. &
Franzini, Joseph B. Water-Resources Engineering (1972)
McGraw-Hill ISBN 0-07-037959-9 pp.454-456
6. ^ World Health
Organization (2004). "Consensus of the Meeting: Nutrient minerals in
drinking-water and the potential health consequences of long-term consumption
of demineralized and remineralized and altered mineral content
drinking-waters."Rolling Revision of the WHO Guidelines for
Drinking-Water Quality (draft). From November 11–13, 2003 meeting in
Rome, Italy at the WHO European Centre for Environment and Health.
7. ^ Goldman, Charles R.
& Horne, Alexander J. Limnology (1983) McGraw-Hill ISBN 0-07-023651-8 chapter 6
8. ^ a b c Franson, Mary Ann (1975). Standard
Methods for the Examination of Water and Wastewater 14th ed.
Washington, DC: American Public Health Association, American Water Works
Association & Water Pollution Control Federation. ISBN 0-87553-078-8
10. ^ Goldman, Charles R.
& Horne, Alexander J. Limnology (1983) McGraw-Hill ISBN 0-07-023651-8 pp.87-88
11. ^ United States
Geological Survey (USGS), Denver, CO (2009). "Definitions of Quality-Assurance Data." Prepared
by USGS Branch of Quality Systems, Office of Water Quality.
12. ^ International Water
Management Institute, Colombo, Sri Lanka (2010). "Helping restore the quality of drinking water after
the tsunami." Success Stories. Issue 7.doi:10.5337/2011.0030
13. ^ World Health
Organization (2011). "WHO technical notes for emergencies." Water
Engineering Development Centre, Loughborough University, Leicestershire, UK.
14. ^ State of California
Environmental Protection Agency Representative Sampling of Ground Water
for Hazardous Substances (1994) pp.23-24
15. ^ For an overview of the
U.S. federal biomonitoring publications, see U.S. EPA,"Whole
Effluent Toxicity."
16. ^ U.S. EPA. Washington,
DC."Methods for Measuring the Acute Toxicity of
Effluents and Receiving Waters to Freshwater and Marine Organisms." Document
No. EPA-821-R-02-012. October 2002.
17. ^ IOWATER (Iowa Department
of Natural Resources). Iowa City, IA (2005). "Benthic Macroinvertebrate Key."
19. ^ Dickens CWS and Graham
PM. 2002. The Southern Africa Scoring System (SASS) version 5 rapid
bioassessment for rivers “African Journal of Aquatic Science”,
27:1-10.
20. ^ "Guidelines for drinking-water quality, fourth
edition". World Health Organization. Retrieved 2 April 2013.
22. ^ International
Organization for Standardization (ISO). "13.060: Water quality". Geneva,
Switzerland. Retrieved 2011-07-04.
24. ^ National Archives,
London, UK. "The Water Supply (Water Quality) Regulations
2000." 2000 No. 3184. 2000-12-08.
25. ^ Republic of South
Africa, Department of Water Affairs, Pretoria (1996). "Water
quality guidelines for South Africa: First Edition 1996."
26. ^ Hodgson K, Manus L. A
drinking water quality framework for South Africa. Water SA. 2006;32(5):673-678 [1][dead link].
28. ^ U.S. Clean Water Act,
Section 303(d), 33
U.S.C. § 1313; Section 305(b), 33
U.S.C. § 1315(b); Section 314, 33
U.S.C. § 1324.
30. ^ Note: Congress
has not provided funds for implementation of the Section 314 Clean Lakes
Program since 1994. See EPA's
Clean Lakes Program.
31. ^ More information about
water quality in the United States is on the EPA's "Surf
Your Watershed" website.
International organizations
·
Drinking water quality guidelines - World
Health Organization
·
The
National River Health Programme - South Africa
Europe
United States
·
U.S. National
Water Quality Monitoring Council (NWQMC) - Partnership of
federal and state agencies
Other organizations
·
NutrientNet,
an online nutrient trading tool developed by the World Resources Institute, designed to
address nutrient-related water quality issues. See also the PA NutrientNet website
designed for Pennsylvania's nutrient trading program.
·
eWater
Cooperative Research Centre - Australian Government funded
initiative supporting water management decision support tools
·
MolluSCAN eye website
designed by the CNRS and the University of Bordeaux, France. Online
biomonitoring of water quality by a 24/7 record of various bivalve molluscs'
behavior and physiology worldwide (biological rhythms, growth rate, spawning,
daily behavior)
