###### Abstract
The first step in the industrial synthesis of PET involves the prepolymerization of dimethyl terephthalate (DMT) or terephthalatic acid (TPA) with ethylene glycol (EG). The reaction leads to the formation of the intermediate compound bis(hydroxyethyl)terephthalate (BHET). Subsequently, polycondensation is carried out to form the polymer. In this process, a catalyst containing elements such as Sb, Ge, or Ti is used [19]. The obtained product exhibits glass-like transparency and good thermal and mechanical properties [19; 20]. It is resistant to various compounds, such as oils, fats, aromatic solvents, chlorinated hydrocarbons, most acids, and diluted alkaline solutions [21]. A significant consequence of PET degradation is the generation of microplastic particles. According to EU legislation [22], microplastic is defined as a small solid object, insoluble in water, or wholly composed of synthetic polymers or chemically modified natural polymers. Microplastic particles have dimensions equal to or less than 5 mm and a length-to-width ratio of 3 or less. Additionally, microplastic fibers are defined as objects with a length equal to or less than 15 mm and a length-to-width ratio greater than three. Sometimes a more precise definition is provided, distinguishing between (i) nanoplastic as particles with the largest dimension ranging from 1 to 1000 nm, (ii) microplastic with dimensions from 1 to 1000 um, (iii) mesoplastic with dimensions from 1 to 10 mm, and (iv) macroplastic with dimensions of 1 cm and larger [23]. To counteract adverse situations effectively, it is essential to understand the mechanisms of PET degradation. These mechanisms vary depending on the degradation pathway and conditions [24]. As a result of degradation, not only can MPs be formed [25] but also different low-molecular-weight chemical compounds can be released [19]. The degradation of PET depends on various factors, including UV radiation [26], the presence of water [25], the presence of additives enhancing the material's properties [27], and even the specific form in which the PET material appears [25]. Factors occurring simultaneously, such as the presence of water combined with exposure to UV radiation, interact synergistically, accelerating the degradation of the material [28]. Previous studies have reported the presence of microplastics in bottled water [29; 30; 31; 32; 33]. However, these findings sometimes differ significantly regarding the composition of the detected microplastic particles. Despite this variability, there is general agreement about their presence. The discrepancies highlight the urgent need for the standardization of detection procedures, covering all stages of analysis--from sample collection and concentration to quantitative determination, shape characterization, and reporting methods [22]. It is also worth noting that matrix effects and the risk of cross-contamination are significant challenges in such analyses. While these issues are less pronounced in the case of bottled water, they still need to be considered carefully. Additionally, the detection of the smallest particles is crucial, yet it continues to pose significant challenges [31]. The fraction of the smallest MPs with sizes below 5 um is considered to be potentially the most hazardous [34]. The aim of this work is to discuss the problem of degradation of polyethylene terephthalate bottles intended for water. The paper aims not only to raise awareness of the importance of this issue but also to highlight potential management strategies and explore the application of solutions. The situation is critical and demands prompt action across various fields. Increasing product stability before use [35; 36] while facilitating waste degradation [37; 38] are two seemingly contradictory approaches, yet their application could be a way to minimize the problem.