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Water quality parameters



Below some parameters used to monitor water quality are described. If you want more details about any of the parameters listed below, please check the references.

To understand better the descriptions below, it’s important know that ion is "any atom or group of atoms that bears one or more positive or negative electrical charges. (...) Ions are formed by the addition of electrons to, or the removal of electrons from, neutral atoms or molecules or other ions; by combination of ions with other particles; or by rupture of a covalent bond between two atoms in such a way that both of the electrons of the bond are left in association with one of the formerly bonded atoms."[1]

Electrical conductivity

"Conductivity is a measure of water’s capability to pass electrical flow. This ability is directly related to the concentration of ions in the water. These conductive ions come from dissolved salts and inorganic materials (...). The more ions that are present, the higher the conductivity of water. Likewise, the fewer ions that are in the water, the less conductive it is. Distilled or deionized water can act as an insulator due to its very low (if not negligible) conductivity value. Sea water, on the other hand, has a very high conductivity."[2]

Conductivity is an indirect way to measure pollutant concentration, and changes in it’s level indicates changes in water composition.[3] Water within the EC range between 0 - 2500 μS/cm can be consumed by humans, although most would prefer water in the lower half of this range if available.[4]

pH

"pH is a measure of how acidic/basic water is."[5] A pH level of 7 is neutral, values "of less than 7 indicate acidity, whereas a pH of greater than 7 indicates a base. pH is really a measure of the relative amount of free hydrogen and hydroxyl ions in the water. Water that has more free hydrogen ions is acidic, whereas water that has more free hydroxyl ions is basic. Since pH can be affected by chemicals in the water, pH is an important indicator of water that is changing chemically."[5]

"The optimum pH will vary in different supplies according to the composition of the water and the nature of the construction materials used in the distribution system."[6] The Brazilian government recommends to keep pH in distributions systems in the range 6.0–9.5.[7]

ORP

"Just as the transfer of hydrogen ions between chemical species determines the pH of an aqueous solution, the transfer of electrons between chemical species determines the"[8] oxidation–reduction potential (ORP, or redox potential) "of an aqueous solution. Like pH, the reduction potential represents how strongly electrons are transferred to or from species in solution."[8]

ORP measures the ability of the water "to cleanse itself or break down waste products, such as contaminants and dead plants and animals. When the ORP value is high, there is lots of oxygen present in the water. This means that bacteria that decompose dead tissue and contaminants can work more efficiently. In general, the higher the ORP value, the healthier the"[9] water is.

"It is possible to define a minimum level of ORP necessary to ensure effective disinfection. This value has to be determined on a case-by-case basis; universal values cannot be recommended. Further research and evaluation of ORP as an operational monitoring technique are highly desirable."[10]

Temperature

"Temperature is an important factor to consider when assessing water quality. In addition to its own effects, temperature influences several other parameters and can alter the physical and chemical properties of water. In this regard, water temperature should be accounted for when determining"[11] (between others):

  • "Conductivity (...)
  • Oxidation reduction potential (ORP)
  • pH"[11]

References

  1. http://global.britannica.com/science/ion-physics
  2. http://www.fondriest.com/environmental-measurements/parameters/water-quality/conductivity-salinity-tds/
  3. http://cetesb.sp.gov.br/aguas-interiores/wp-content/uploads/sites/32/2013/11/variaveis.pdf (in Portuguese)
  4. http://agriculture.vic.gov.au/agriculture/farm-management/soil-and-water/salinity/measuring-the-salinity-of-water
  5. http://water.usgs.gov/edu/ph.html
  6. http://www.who.int/water_sanitation_health/dwq/chemicals/en/ph.pdf
  7. http://site.sabesp.com.br/uploads/file/asabesp_doctos/kit_arsesp_portaria2914.pdf (in Portuguese)
  8. https://en.wikipedia.org/wiki/Reduction_potential
  9. http://www.enr.gov.nt.ca/sites/default/files/oxidation-reduction_potential.pdf
  10. http://www.who.int/water_sanitation_health/dwq/fulltext.pdf?ua=1
  11. http://www.fondriest.com/environmental-measurements/parameters/water-quality/water-temperature/

water-quality-monitoring water-quality conductivity open-water ph

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