## 1 Introduction  
Drinking water is a necessary but scarce good. Despite the fact that water is the most abundant and common substance on our planet--as it covers 70% of its surface--96.5% of it is contained in the oceans. Of the remaining 3.5%, approximately 2.5% is found in the polar ice caps and glaciers and only 0.61% is liquid fresh water. Of the latter, around 0.98% is found in underground aquifers, which are difficult to access, while only 0.009% constitutes fresh surface water (rivers and lakes). Furthermore, only 0.003% of the total is fresh water available to be used for residential purposes. That is, if the Earth's total water were a 100 L container, only half a teaspoon of water would be suitable for human consumption [1]. The sources of water pollution can be natural (rain, decomposing vegetable matter, soil erosion, etc.) or anthropogenic (activity livestock, by-products of industrial activity, home waters, etc. ), but both give rise to water that does not meet the necessary requirements to ensure its potability. The basic water treatment processes include several stages: coagulation, flocculation, particle separation (sedimentation/flotation), filtration, and disinfection (chlorination/ozonation) [2]. In many of these stages, the addition of chemicals into the flow of water to be treated is performed, and it is at this very point that this research provides a contribution with respect to correct dosage and control. Of all the treatments mentioned above, this paper focuses on disinfection. This process attempts to destroy or inactivate pathogenic organisms present in water, mainly bacteria, viruses, and protozoa [3]. Disinfection treatments can be physical (gamma radiation, X-rays, ultraviolet radiation, thermal sterilization, etc.) or chemical (heavy metals, acids or bases, halogens, ozone, permanganate, etc. ), with the latter being the most common form of treatment. Among the chemical reagents, chlorine and its derived compounds are the most widely used disinfecting agents worldwide. Many organisms regulate the residual chlorine values and they depend on the end use of the water. Thus, for drinking water, it is recommended that the residual free chlorine be between 0.2 and 1 ppm (parts per million), while in the case of swimming pools and spas, it should be kept between 1.5-3.0 ppm. However, these values are general and each competent body has determined its own thresholds. The use of chlorine as a disinfecting agent began in the early 20 th century and went on to complete the filtration process, which was already widely used. The most common chlorine family products for water disinfection are chlorine gas, chloramines, sodium hypochlorite, and calcium hypochlorite. Chlorine (Cl\({}_{2}\)) is a yellowish green, denser than air, toxic gas. It is a very oxidizing product that reacts with many compounds [4]. In fact, the most widely used chemical in the world is chlorine. In the presence of humidity, chlorine is extremely corrosive and therefore the conduits and the materials in contact with it must be made of special alloys. Chlorine vapor is irritating by inhalation and can cause serious injury if exposed to high concentrations. Chlorine management must therefore be carried out by specialized staff, and very effective control and alarm systems are necessary. For these reasons, the use of hypochlorites in solution or in solid form is preferable. Sodium hypochlorite (NaClO) in solution is a disinfectant that has been used since the 18 th century and is popularly known as bleach. At an industrial level, it is obtained by reacting chlorine gas with a sodium hydroxide solution. After the reaction, greenish yellow aqueous solutions are obtained, which have a determined concentration of active chlorine per liter [5]. It is marketed in solutions with concentrations between 3% and 15% by weight. Sodium hypochlorite is a very powerful and unstable oxidant, and thus a solution of 100 g of active chlorine per liter, after being stored for 3 months, can contain 90 g or even less.