Wikipedia

Raw water

Raw wateris water found in the environment that has not beentreatedand does not have any of its minerals, ions, particles, bacteria, or parasites removed. Raw water includesrainwater,ground water,water from infiltration wells, and water from bodies likelakesandrivers.

Raw water is generally unsafe for human consumption due to the presence of contaminants. A major health problem in somedeveloping countriesis use of raw water for drinking and cooking.[1]

Without treatment, raw water can be used forirrigation,construction,or cleaning purposes.[2]Farmers use it for watering theircropsand give it tolivestockto drink, storing it in man-made lakes or reservoirs for long periods of time. Construction industries can use raw water for makingcementor for damping down unsealed roads to prevent dust rising. Raw water can also be used for flushing toilets and washing cars, as well as any other purposes that do not require it to be consumed by humans. Water in this form is considered raw, as opposed to water which has beentreatedbefore consumption, such asdrinking wateror water which has been used in an industrial process, such aswaste water.

Raw water flushingis a method ofwater conservationwhere raw water is used for flush toilets.

Composition

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The composition of raw water is naturally variable, but commonly contains one or more of the following significant contaminants, in the form of dissolved ions, particles and living organisms:[3]

Other, less common, contaminants of raw water include:

These contaminants can be harmful to humans if they drink raw water containing them, or if the water is not treated properly before consumption. The contaminants can also have an effect on the local ecosystem. For example, endocrine disrupting chemicals can have harmful effects on fish populations living in naturallakesandrivers.[7]These growing health concerns have led to the development of guidelines, such HACCP (Hazard Analysis and Critical Control Points), for the production of safe drinking water from wastewater and raw water, and research intosustainablewater supply alternatives.[8][9]

Treatment

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Main article:Water treatment
Water treatment plant of Bragança, Portugal

Raw water can be used for many purposes, such ascooling water,water forrinsingandchemicalproduction,purified water,anddrinking water.[10]However, due to the possiblecontaminants,raw water must be treated before it is allowed for human consumption or industrial use.[11]There are several steps involved in the treatment of raw water, and different methods in which it can take place.

Reverse osmosis

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Reverse osmosishas been used for the production of demineralised water for over 30 years.[10]In reverse osmosis, water is transported across amembraneunder high pressure, leaving a product that consists mainly of water and aconcentratecontaining most other components such asmineralsand unwantedresidues.[12]Many contaminants, includingiron,manganese,ammonium,traces ofpesticidesandmedicines,organic micro pollutants, andradioactiveparticles can be removed with reverse osmosis alone.[4][12]This efficiency has made reverse osmosis the primary method ofwater purification,often being used in combination with other methods, as a final treatment. A downside to reverse osmosis is that the removing of most minerals from water can have negative effects on its taste.[12]Minerals are sometimes added to drinking water that was already filtered to improve its taste.

Conventional pre-treatment

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The conventional treatment method for water purification is a complex, multistage process that was used for many years.[10]It generally consists of five primary steps.[11]First, raw water is adjusted foralkalinityandpHwith the addition of hydratedlimeandcarbon dioxide.Second, particulate matter is congregated withaluminum sulphateand othercoagulants,such aspolymers,which the water flows in a cascade that mixes the chemicals and raw water with the coagulants. Third, the water is slowly mixed inclarifierswhere larger particles settle down to the bottom and are periodically removed (sedimentation). Fourth, water is directed from the clarifiers to the filters (e.g.anthraciteandsand filter) to entrap any smaller particles that survived the clarification process. Finally,sodium hydroxideis added to adjust the final pH/alkalinity,sodium hypochloritefordisinfectionandfluorideforfluoridation.This process is often used as a pre-treatment method while another processes, such as reverse osmosis, is used for the final treatment.[10] A disadvantage of this method is its use of chemicals, such asozone,flocculents,hydrogen peroxide,lime, andchlorinefor the filtration process.[10]These chemicals could be dangerous if used incorrectly or if they remained in the water after complete treatment. This requires special precautions, and each step of the process has to be controlled to achieve an overall optimal performance.[10]The need for a complex control system for conventional treatment can result in it being financially costly.[10]This has led to the development of alternative pre-treatment and treatment methods for raw water.

Ultrafiltration

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Drinking water treatment of 300 m3/h using ultrafiltration in Grundmühle waterworks (Germany)

Ultrafiltrationis amembrane filtrationprocess and provides an alternative to conventional pre-treatment.[10]In this method water is only pre-filtered with a commonscreen filterbefore being filtered at high pressure through a membrane, separating the water from contaminants within it. Ultrafiltration can be used on its own for water purification or as a pre-treatment for reverse osmosis. Its advantages over conventional pre-treatment include: very highwater qualityindependent of the contaminants in the initial raw water, a plant that is simpler in design and more flexible, which makes it easier to automate, lower use ofchemicals,and final product free ofvirusesandmicroorganisms.

Biofilm pre-treatment and Bio-diatomite Dynamic Membrane Reactor

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Thebiofilmmembrane filtration method is used to remove harmful chemical by-products, such as NH4+-N, totalnitrogen,anddissolved organic matter,that could form from disinfection processes.[13]Biofilm Pre-treatment is a necessary step for water treatment in many parts of world due to its low operation cost and effectiveness atpollutantremoval. In this process microorganisms remove contaminants in raw and wastewater that are harmful to humans, but nutrients to them.[13]Bio-diatomite dynamicmembranereactor filtration combines dynamic membrane technology forwastewater treatment,and microbial colonies that formdiatomiteparticles topurifywater.[14]These methods are under development inChinaas part of addressing the country'spollutionproblems.

Turbidity

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Turbid water

Turbidityis how murky orhazywater seems due tosuspendedparticles.The more suspended particles, the higher the turbidity. Turbidity is used to visually measure water quality, being most common in unfiltered raw water.[15] High amounts of turbidity in raw water can occur due to:[15]

  • Increased flow due to heavy rain fall
  • Spring turnover of water masses
  • Bankerosion
  • Sedimentresuspension in shallow areas
  • Temporary increase from the more turbid areas

Turbidity and health concerns

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During high turbidity peaks,pathogensare more commonly found in raw water. This can contribute to the spread ofillnesses.[16]When turbidity increases, reported hospital visits for the elderly (65+) with gastrointestinal illnesses also increase. Even places with water filtration systems that meet standards can have anendemicofgastrointestinal illness,orwaterborneinfectious diseases.Those hospitalized represent a small percentage of totalmorbiditycaused by these illnesses.[9]

Controlling turbidity

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Controlling the land surrounding raw water reservoirs and other sources is key to reducing turbidity. Areas of high sediment resuspension and erosion need attending regularly, and screens and other devices are needed to catch suspended particles. Screens that trap particles anddebrismust be cleaned consistently. Flushing out water pumps should be done when demand is lowest. This gives time for the water to settle, and decrease turbidity before is it needed in high amounts. "Turbidity reduction is best achieved when the water is run through a series of chemical and physical treatment methods before reaching the filter".[17]

Waterside of Saint Lawrence River near Kamouraska

Raw water dieting

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See also:Raw foodism

Around 2017, untreated spring water, described as "naturally probiotic" raw water, became a commercial product distributed through health food shops, but experts have raised public health concerns about the possible occurrence of harmful bacteria, viruses, and parasites such asGiardia.The products are associated with afad dietof "raw waterfasting",[18][19]reportedly finding purchase among the "health-conscious elite" ofSilicon Valley,including figures such as theraw veganfounder ofJuiceroDoug Evens.[20][21]One doctor compared the movement'srejection of established scienceto theanti-vaccination movement.[22]One raw water business in the United States has even claimed that methods used by bottled and spring water producers couldchange the molecular structure of water.[23][24]

The fad was mocked onThe Daily Showin April 2018 in a segment that included an interview withMarion Nestle.[25][26]

See also

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References

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  1. ^Huq, A; et al. (July 1996)."A simple filtration method to remove plankton-associated Vibrio cholerae in raw water supplies in developing countries".Applied and Environmental Microbiology.62(7): 2508–2512.Bibcode:1996ApEnM..62.2508H.doi:10.1128/AEM.62.7.2508-2512.1996.PMC168033.PMID8779590.
  2. ^Perth W.A. (2016) What is Raw Water?. Vintage Road Haulage.http:// vintageroadhaulage.au/faq/what-is-raw-water/
  3. ^Safe Drinking Water Committee (1980), "Raw water quality",Drinking Water and Health,vol. 2, National Academies, pp. 7 et seq
  4. ^abManu, A., Santhanakrishnan, V., Rajaram, S., & Ravi, P. M. (2014). Concentration of natural radionuclides in raw water and packaged drinking water and the effect of water treatment. Journal of Environmental Radioactivity, 138, 456-459
  5. ^Happonen, M., Koivusalo, H., Malve, O., Perkola, N., Juntunen, J., & Huttula, T. (2016). Contamination risk of raw drinking water caused by PFOA sources along a river reach in south-western finland. Science of the Total Environment, 541, 74-82
  6. ^Falconer, I. R. (2006). Are Endocrine Disrupting Compounds a Health Risk in Drinking Water? International Journal of Environmental Research and Public Health, 3(2), 180–184
  7. ^Mills, L. J., & Chichester, C. (2005). Review of evidence: Are endocrine-disrupting chemicals in the aquatic environment impacting fish populations? Science of the Total Environment, 343(1–3), 1-34
  8. ^Dewettinck T, van Houtte E, Geenens D, van Hege K, Verstraete W. HACCP (Hazard analysis and critical control points) to guarantee safe water reuse and drinking water production. A case study. Water Sci. Technol. 2001; 43: 31–38
  9. ^abRodriguez, C., Van Buynder, P., Lugg, R., Blair, P., Devine, B., Cook, A., & Weinstein, P. (2009). Indirect Potable Reuse: A Sustainable Water Supply Alternative. International Journal of Environmental Research and Public Health, 6(3), 1174–1209
  10. ^abcdefghClever, M., Jordt, F., Knauf, R., Räbiger, N., Rüdebusch, M., & Hilker-Scheibel, R. (2000). Process water production from river water by ultrafiltration and reverse osmosis. Desalination, 131(1–3), 325-336
  11. ^abBertone, E., Stewart, R. A., Zhang, H., & O'Halloran, K. (2016). Hybrid water treatment cost prediction model for raw water intake optimization. Environmental Modelling & Software, 75, 230-242
  12. ^abcVingerhoeds, M. H., Nijenhuis-de Vries, M. A., Ruepert, N., van der Laan, H., Bredie, W. L. P., & Kremer, S. (2016). Sensory quality of drinking water produced by reverse osmosis membrane filtration followed by remineralisation. Water Research, 94, 42-51
  13. ^abYang, G., Feng, L., Wang, S., Zhou, J., Guo, C., Xia, T., Sun, W., Jiang, Y., Sun, X., Cao, Lian., Xu, X., Zhu, L. (2015). Potential risk and control strategy of biofilm pretreatment process treating raw water. Bioresource Technology, 198, 456-463
  14. ^Chu, H., Cao, D., Dong, B., & Qiang, Z. (2010). Bio-diatomite dynamic membrane reactor for micro-polluted surface water treatment. Water Research, 44(5), 1573-1579
  15. ^abGauthier, V., Barbeau, B., Tremblay, G., Millette, R., & Bernier, A. (2003). Impact of raw water turbidity fluctuations on drinking water quality in a distribution system. Journal of Environmental Engineering and Science, 2(4), 281-291
  16. ^Schwartz, J., Levin, R., & Goldstein, R. (2000). Drinking water turbidity and gastrointestinal illness in the elderly of Philadelphia. Journal of Epidemiology and Community h, 54(1), 45–51
  17. ^Satterfield, Z. (2006). Turbidity Control. Tech Brief, 6(2), 1-4
  18. ^Bever, Lindsey."Why 'raw water' could help you lose weight, in a bad way",Sydney Morning Herald,4 January 2018.
  19. ^Mosia,Lebohang."Why is there such a thirst among influencers for ‘raw water’?",Independent Online,10 November 2022.
  20. ^Turton, William."The Juicero founder is really into raw water",Vice News,7 March 2018.
  21. ^Mole, Beth."Meet “raw” water—ludicrously priced unfiltered water with random bacteria ",Ars Technica,2018.
  22. ^Morris, David Z."Silicon Valley’s Next Big Idea: Untreated Drinking Water",Fortune,31 December 2017.
  23. ^Bever, Lindsey (4 January 2018)."'Raw water' is the latest health craze. Here's why drinking it may be a bad idea ".Washington Post.Retrieved4 January2018.
  24. ^Bowles, Nellie (29 December 2017)."Unfiltered Fervor: The Rush to Get Off the Water Grid".The New York Times.
  25. ^"Video: A Deep Dive into the" Raw Water "Craze - The Daily Show with Trevor Noah (Video Clip)".Comedy Central. 18 April 2018. Archived fromthe originalon April 22, 2018.
  26. ^"A Deep Dive Into The" Raw Water "Craze — The Daily Show (YouTube)".YouTube.30 March 2022.

Additional sources

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