## 1 Introduction  
On 11 March 2020, the World Health Organization (WHO) declared COVID-19 a pandemic. This infectious disease is caused by a new strain of CoV, a mutation (ID-19) of its two previous forms and is called SARS-CoV-2 or CoV-19 [1]. During the pandemic of COVID-19, national and international medical organizations around the world treated or alleviated symptoms, in certain hospitalized patients, by using some drugs such as chloroquine, HCQ, azithromycin, ivermectin, dexamethasone, remdesivir, favipiravir and some HIV antivirals [2]. However, the possible use of some of them to treat COVID-19 is only an unproven hypothesis, such as the case of chloroquine and HCQ [3]. In some countries, the use of some of these drugs on large scale during the pandemic was reported, for example, in Italy [4] and Brazil [5]. Consequently, the high risk of water contamination due to their large production and utilization is a key issue to overcome urgently. Sometimes these drugs are not completely metabolized by the body, and their active forms or metabolites can be eliminated through feces and urine [6]. After that, these compounds reach the sewage system when discharged. At that point, some limitations are found in their elimination from water treatment plants which mostly rely on conventional treatment systems in industrialized countries, but it is different in developing nations since they are under different pressures where the pollutants are not efficiently treated or have limitations in the removal of these compounds, provoking environmental and health risks [7; 8; 9; 10; 11]. In Brazil, HCQ was included in COVID-19 kits together with ivermectin and azithromycin, as a pre-treatment option [12]. Recent studies have demonstrated that HCQ is present in Brazilian water ecosystems, confirming its high persistence and bioaccumulation in vegetation and groundwater [13]. Therefore, it has motived some investigations to develop sensors for quantifying and monitoring HCQ to determine its potential as contaminant as well as the search for an effective approach to remove this micropollutant from wastewaters before its discharge in water ecosystems [14]. Based on the existing literature, the treatment of different water matrices (synthetic or real) containing HCQ has been carried out by photolysis [15], adsorption [16; 17], photo-catalysis [18] and electrochemical technologies (electrooxidation (EO), photo-assisted EO and sono-assisted EO) using boron doped diamond (BDD) [19]. However, no real matrices polluted with HCQ were treated in the case of electrochemical treatments. Considering that several research groups are evaluating the treatment effectiveness of certain technologies by polluting in laboratory different water matrices (e.g., river, sea, groundwater, tap water, drinking water and so on) with a well-known amount of a single target pollutant for understanding the experimental data in order to translate to real applications [20]. Then, this work aims to electrochemically treat a real water matrix polluted with HCQ. To do that, (i) real water samples were collected and preserved, (ii) identification and quantification of HCQ in these water samples was spectrophotometrically and electroanalytically performed and (iii) EO approach in a batch reactor with BDD anode was tested to decontaminate a real water matrix. In a previous work, the use of the cork-graphite composite as electrochemical sensor for quantifying HCQ in real water matrices [14] was demonstrated, confirming HCQ pollution in lagoon water. However, the possibility to integrate technologies as an appropriate water depollution solution to eliminate HCQ from a real water matrix was not proven yet. Therefore, the development of technologies and smart water solutions to reach the Sustainable Development Goal 6 (SDG6) represent a substantial opportunity to guarantee sustainability and increase competence in water management (to treat and distribute water for human use) [21].