Disinfecting water is considered as a main public health conquering since it considerably decreased waterborne illness and augmented life expectancy . Nevertheless, a not planned sequel was the formation of disinfection by-products (DBPs), which are generated via the reaction of disinfectants (chlorine, chloramine, ozone, chlorine dioxide, ultraviolet (UV)) with natural and anthropogenic organic matter, bromide, and iodide   . Such compounds are produced for any specific objective but are generated throughout water treatment   . Until now, more than 700 DBPs have been defined, and of those, around only 100 have been strictly examined for their existence, generation, and quantitative analytical biological toxicity   .
In the early 1970s, at most a few of DBPs were investigated, foremost trihalomethanes (THMs)  . Later, such THMs were observed to be prevalent in chlorinated water and were as well discovered to be carcinogenic in laboratory animals  . Consequently, the earliest DBP regulations were announced   . The emerging U.S. Environmental Protection Agency (EPA), which was instituted in 1970, started to regulate THMs (chloroform, bromoform, bromodichloromethane, and chlorodibromomethane) below the 1979 Safe Drinking Water Act . Subsequently, more toxicity facts were acquired for five haloacetic acids, bromate, and chlorite; and these were attached to the regulation below the Stage 1 and Stage 2   . The World Health Organization, European Union, and many different nations also have guidelines or regulations for some DBPs in drinking water .
This work focuses on the hard challenges in dealing with the disinfection by-products (DBPs). Fundamental interrogations relating DBPs monitoring are presented. The fact that regulating DBPs is important or not is also discussed.
2. Deep and Basic Questions
Richardson and Plewa , well-known experts in the DBPs field, posted a relevant question: “Are we controlling the right DBPs?” Previous researches on human epidemiology support the plan of regulating and controlling DBPs since numerous investigations noted a hazard of bladder cancer, colorectal cancer, miscarriage, and birth defects   .
One more matter in question is that water is not as it was consumed seventy years earlier   . It is ever-changing   . During the time that regulations and ecological protection actions greatly enhanced the protection of water, potable water is unlike what it was a half-century ago   .
If in the end all the different DBPs were as well decreased with the regulated DBPs, the situation would be better . In fact, the more poisonous iodo-DBPs and nitrogen-containing DBPs (N-DBPs)  could be produced at much greater degrees when plants change to chloramine . A change to ozone could as well lead to an augmented generation of bromate, as well as unregulated halonitromethane, haloaldehyde, haloketone, and haloacid DBPs, with secondary chlorination   . Paradoxically, UV could response with natural organic matter (NOM) to augment the production of considerably hazardous halonitromethanes if secondary chlorine is implemented   . Since ozone and UV do not provide a residual disinfectant, chlorine or chloramine is frequently injected as an additional disinfectant to keep disinfection in the distribution system   .
Additional elements also influence water sources like population increases, climate change, water usage, and wastewater reuse   . As an example, climate change increases wastewater pollutants in water sources, as well as concentrates NOM, bromide, and iodide, constituting circumstances for worsening the hazardous effects on water     .
3. DBPs Toxicity: Regulating DBPs Significance
Since the earliest DBP poisoning investigations launched five decades ago, more than 100 additional DBPs were rigorously analyzed for cytotoxicity, genotoxicity, endocrine disruption, and carcinogenicity   . Several unregulated DBPs were found more dangerous than regulated ones   .
More technical details can be found in the excellent discussion performed by Richardson et al.  and references cited in.
Finally, treatment master plans must be adopted to avoid the formation of DBPs, whether regulated or unregulated   . Viable techniques involving the usage of granular activated carbon or membranes to retain DBP precursors (then injecting a smaller injection of chlorine for killing pathogens), utilizing UV pursued by a smaller dosage of chlorine    (Figure 1).
Considered as the latest technique, post-disinfection is extremely crucial for the classical potable water treatment   . Disinfection target is to kill microorganisms that cause diseases in water to make certain the potable water security   . But, the quality of the fountainhead water becomes worse and worse due to rising natural and artificial water contaminations   . DBPs are generated at what time disinfectants (chlorine, chlorine dioxide, chloramines or ozone) interact with NOM, anthropogenic contaminants, bromide, and iodide in the potable water treatment chain   . As well the regulated DBPs (such as THMs, HAAs, bromate and chlorite), several additional unregulated DBPs have been detected   . Nitrosoamines are the elements of these new DBPs, which are strongly carcinogenic, mutagenic, and teratogenic   . The main points drawn from this review may be drawn as:
1) The first objective of water treatment is to render water secure to consume by making certain that it is without of pathogens and poisonous compounds; the second target is to render it a desirable drink by eliminating unwanted turbidity, tastes, colors, and odors   . Considering the first objective render
Figure 1. Regulated DBPs vs. unregulated DBPs .
water without pathogens and toxic matters, it is obvious that disinfecting by injecting chemicals is an impossible compromise since disinfection kills microorganisms but forms DBPs  . Consequently, injecting chemical products into water must be avoided even if the mentioned reason is disinfecting water  .
2) Instead of chemical therapy, sure techniques such as physical processes like distillation and membrane processes should be urgently adopted to remove pathogens and organic compounds  .
3) Finally, at the COVID-19 period, this study arrives at its time since the Environmental Engineers and the Green Chemistry specialists have largely opened the discussion about polluting industry and preserving nature    .
This research has been funded by the Research Deanship of University of Ha’il, Saudi Arabia, through the Project RG-191190.
 Richardson, S.D. and Plewa, M.J. (2020) To Regulate or Not to Regulate? What to Do with More Toxic Disinfection Byproducts? Journal of Environmental Chemical Engineering, 8, Article ID: 103939. https://doi.org/10.1016/j.jece.2020.103939
 Ghernaout, D., Naceur, M.W. and Aouabed, A. (2011) On the Dependence of Chlorine By-Products Generated Species Formation of the Electrode Material and Applied Charge during Electrochemical Water Treatment. Desalination, 270, 9-22.
 Boucherit, A., Moulay, S., Ghernaout, D., Al-Ghonamy, A.I., Ghernaout, B., Naceur, M.W., Ait Messaoudene, N., Aichouni, M., Mahjoubi, A.A. and Elboughdiri, N.A. (2015) New Trends in Disinfection By-Products Formation upon Water Treatment. Journal of Research & Developments in Chemistry, 2015, Article ID: 628833. https://doi.org/10.5171/2015.628833
 Ghernaout, D. and Elboughdiri, N. (2020) Strategies for Reducing Disinfection By-Products Formation during Electrocoagulation. Open Access Library Journal, 7, e6076.
 Richardson, S.D., Plewa, M.J., Wagner, E.D., Schoeny, R. and DeMarini, D.M. (2007) Occurrence, Genotoxicity, and Carcinogenicity of Regulated and Emerging Disinfection By-Products in Drinking Water: A Review and Roadmap for Research. Mutation Research, 636, 178-242. https://doi.org/10.1016/j.mrrev.2007.09.001
 Richardson, S.D. and Postigo, C. (2015) Formation of DBPs: State of the Science. In: Karanfil, T., Mitch, W.A., Westerhoff, P. and Xie, Y., Eds., Recent Advances in Disinfection By-Products, Am. Chem. Society, Washington DC, 189-214. https://doi.org/10.1021/bk-2015-1190.ch011
 Duirk, S.E., Lindell, C., Cornelison, C., Kormos, J.L., Ternes, T.A., Attene-Ramos, M.S., Osiol, J., Wagner, E.D., Plewa, M.J. and Richardson, S.D. (2011) Formation of Toxic Iodinated Disinfection By-Products from Compounds Used in Medical Imaging. Environmental Science & Technology, 45, 6845-6854. https://doi.org/10.1021/es200983f
 Li, X.F. and Mitch, W.A. (2018) Drinking Water Disinfection Byproducts (DBPs) and Human Health Effects: Multidisciplinary Challenges and Opportunities. Environmental Science & Technology, 52, 1681-1689. https://doi.org/10.1021/acs.est.7b05440
 Bellar, T.A., Lichtenberg, J.J. and Kroner, R.C. (1974) The Occurrence of Organohalides in Chlorinated Drinking Waters. Journal of the American Water Works Association, 66, 703-706.
 Ghernaout, D. and Elboughdiri, N. (2020) Controlling Disinfection By-Products Formation in Rainwater: Technologies and Trends. Open Access Library Journal, 7, e6162.
 Ghernaout, D. (2018) Disinfection and DBPs Removal in Drinking Water Treatment: A Perspective for a Green Technology. International Journal of Advances in Applied Sciences, 5, 108-117. https://doi.org/10.21833/ijaas.2018.02.018
 Ghernaout, D., Alghamdi, A., Aichouni, M. and Touahmia, M. (2018) The Lethal Water Tri-Therapy: Chlorine, Alum, and Polyelectrolyte. World Journal of Applied Chemistry, 3, 65-71.
 Ghernaout, D., Aichouni, M. and Touahmia, M. (2019) Mechanistic Insight into Disinfection by Electrocoagulation—A Review. Desalination and Water Treatment, 141, 68-81.
 Ghernaout, D., Elboughdiri, N., Alghamdi, A. and Ghernaout, B. (2020) Trends in Decreasing Disinfection By-Products Formation during Electrochemical Technologies. Open Access Library Journal, 7, e6337. https://doi.org/10.4236/oalib.1106337
 Ghernaout, D., Elboughdiri, N., Ghareba, S. and Salih, A. (2020) Coagulation Process for Removing Algae and Algal Organic Matter—An Overview. Open Access Library Journal, 7, e6272.
 Ghernaout, D., Ghernaout, B. and Kellil, A. (2009) Natural Organic Matter Removal and Enhanced Coagulation as a Link between Coagulation and Electrocoagulation. Desalination and Water Treatment, 2, 203-222. https://doi.org/10.5004/dwt.2009.116
 Ghernaout, D., Naceur, M.W. and Ghernaout, B. (2011) A Review of Electrocoagulation as a Promising Coagulation Process for Improved Organic and Inorganic Matters Removal by Electrophoresis and Electroflotation. Desalination and Water Treatment, 28, 287-320.
 Ghernaout, D. (2017) Environmental Principles in the Holy Koran and the Sayings of the Prophet Muhammad. American Journal of Environmental Protection, 6, 75-79.
 Plewa, M.J., Wagner, E.D., Muellner, M.G., Hsu, K.M. and Richardson, S.D. (2008) Comparative Mammalian Cell Toxicity of N-DBPs and C-DBPs. In: Karanfil, T., Krasner, S.W., Westerhoff, P. and Xie, Y., Eds., Occurrence, Formation, Health Effects and Control of Disinfection By-Products in Drinking Water, American Chemical Society, Washington DC, 36-50.
 Krasner, S.W., Weinberg, H.S., Richardson, S.D., Pastor, S.J., Chinn, R., Sclimenti, M.J., Onstad, G.D. and Thruston Jr., A.D. (2006) The Occurrence of a New Generation of Disinfection By-Products. Environmental Science & Technology, 40, 7175-7185.
 Reckhow, D.A., Linden, K.G., Kim, J., Shemer, H. and Makdissy, G. (2010) Effect of UV Treatment on DBP Formation. Journal of the American Water Works Association, 102, 100-113. https://doi.org/10.1002/j.1551-8833.2010.tb10134.x
 Ghernaout, D. and Elboughdiri, N. (2020) UV-C/H2O2 and Sunlight/H2O2 in the Core of the Best Available Technologies for Dealing with Present Dares in Domestic Wastewater Reuse. Open Access Library Journal, 7, e6161. https://doi.org/10.4236/oalib.1106161
 Ghernaout, D., Moulay, S., Ait Messaoudene, N., Aichouni, M., Naceur, M.W. and Boucherit, A. (2014) Coagulation and Chlorination of NOM and Algae in Water Treatment: A Review. International Journal of Environmental Monitoring and Analysis, 2, 23-34.
 Ghernaout, D. and Ghernaout, B. (2010) From Chemical Disinfection to Electrodisinfection: The Obligatory Itinerary? Desalination and Water Treatment, 16, 156-175.
 Ghernaout, D. (2017) Water Reuse (WR): The Ultimate and Vital Solution for Water Supply Issues. International Journal of Sustainable Development Research, 3, 36-46.
 Ghernaout, D., Alshammari, Y., Alghamdi, A., Aichouni, M., Touahmia, M. and Ait Messaoudene, N. (2018) Water Reuse: Extenuating Membrane Fouling in Membrane Processes. International Journal of Environmental Chemistry, 2, 1-12. https://doi.org/10.11648/j.ajche.20180602.12
 Ghernaout, D., Elboughdiri, N. and Ghareba, S. (2019) Drinking Water Reuse: One-Step Closer to Overpassing the “Yuck Factor”. Open Access Library Journal, 6, e5895.
 Ghernaout, D., Elboughdiri, N. and Alghamdi, A. (2019) Direct Potable Reuse: The Singapore NEWater Project as a Role Model. Open Access Library Journal, 6, e5980.
 Wagner, E.D. and Plewa, M.J. (2017) CHO Cell Cytotoxicity and Genotoxicity Analyses of Disinfection By-Products: An Updated Review. Journal of Environmental Sciences, 58, 64-76.
 Ghernaout, D. and Elboughdiri, N. (2020) Removing Antibiotic-Resistant Bacteria (ARB) Carrying Genes (ARGs): Challenges and Future Trends. Open Access Library Journal, 7, e6003.
 Ghernaout, D. (2013) The Best Available Technology of Water/Wastewater Treatment and Seawater Desalination: Simulation of the Open Sky Seawater Distillation. Green and Sustainable Chemistry, 3, 68-88. https://doi.org/10.4236/gsc.2013.32012
 Ghernaout, D. (2014) The Hydrophilic/Hydrophobic Ratio vs. Dissolved Organics Removal by Coagulation—A Review. Journal of King Saud University—Science, 26, 169-180.
 Ghernaout, B., Ghernaout, D. and Saiba, A. (2010) Algae and Cyanotoxins Removal by Coagulation/Flocculation: A Review. Desalination and Water Treatment, 20, 133-143.
 Mian, H.R., Hu, G., Hewage, K., Rodriguez, M.J. and Sadiq, R. (2018) Prioritization of Unregulated Disinfection By-Products in Drinking Water Distribution Systems for Human Health Risk Mitigation: A Critical Review. Water Research, 147, 112-131.
 Ghernaout, D. and Ghernaout, B. (2012) On the Concept of the Future Drinking Water Treatment Plant: Algae Harvesting from the Algal Biomass for Biodiesel Production—A Review. Desalination and Water Treatment, 49, 1-18. https://doi.org/10.1080/19443994.2012.708191
 Ghernaout, D., Badis, A., Braikia, G., Mataam, N., Fekhar, M., Ghernaout, B. and Boucherit, A. (2017) Enhanced Coagulation for Algae Removal in a Typical Algeria Water Treatment Plant. Environmental Engineering and Management Journal, 16, 2303-2315.
 Ghernaout, D. (2018) Magnetic Field Generation in the Water Treatment Perspectives: An Overview. International Journal of Advances in Applied Sciences, 5, 193-203.
 Ghernaout, D., Aichouni, M. and Alghamdi, A. (2018) Applying Big Data (BD) in Water Treatment Industry: A New Era of Advance. International Journal of Advances in Applied Sciences, 5, 89-97. https://doi.org/10.21833/ijaas.2018.03.013
 Ghernaout, D., Alshammari, Y. and Alghamdi, A. (2018) Improving Energetically Operational Procedures in Wastewater Treatment Plants. International Journal of Advances in Applied Sciences, 5, 64-72. https://doi.org/10.21833/ijaas.2018.09.010
 Al Arni, S., Amous, J. and Ghernaout, D. (2019) On the Perspective of Applying of a New Method for Wastewater Treatment Technology: Modification of the Third Traditional Stage with Two Units, One by Cultivating Microalgae and Another by Solar Vaporization. International Journal of Environmental Sciences & Natural Resources, 16, Article ID: 555934.
 Alshammari, Y., Ghernaout, D., Aichouni, M. and Touahmia, M. (2018) Improving Operational Procedures in Riyadh’s (Saudi Arabia) Water Treatment Plants Using Quality Tools. Applied Engineering, 2, 60-71.
 Ghernaout, D., Elboughdiri, N., Ghareba, S. and Salih, A. (2020) Electrochemical Advanced Oxidation Processes (EAOPs) for Disinfecting Water—Fresh Perspectives. Open Access Library Journal, 7, e6257. https://doi.org/10.4236/oalib.1106257
 Ghernaout, D., Elboughdiri, N., Ghareba, S. and Salih, A. (2020) Disinfecting Water with the Carbon Fiber-Based Flow-Through Electrode System (FES): Towards Axial Dispersion and Velocity Profile. Open Access Library Journal, 7, e6238. https://doi.org/10.4236/oalib.1106238
 Belhout, D., Ghernaout, D., Djezzar-Douakh, S. and Kellil, A. (2010) Electrocoagulation of a Raw Water of Ghrib Dam (Algeria) in Batch Using Iron Electrodes. Desalination and Water Treatment, 16, 1-9. https://doi.org/10.5004/dwt.2010.1081
 Ghernaout, D. and Ghernaout, B. (2012) Sweep Flocculation as a Second Form of Charge Neutralisation—A Review. Desalination and Water Treatment, 44, 15-28.