## 4 Microfiber Incidence in Tap Water  
As the global population grows and the environment becomes further affected by climate change, the problem of water scarcity will accelerate and access to fresh drinking water will dwindle. Addressing the crisis of water scarcity is one of the major challenges of the current world [162; 175]. Access to safe water is clearly essential for human health and well-being and, as commented before, safe drinking water is obtained by the purification of water from freshwater bodies in DWTPs [175]. During this process, the elimination of water pollutants that are potentially harmful to human health is essential, and MPs are one of these pollutants [175]. The analysis of MPs in tap water was carried out in several countries and reported data are summarised in Table 4. DWTPs can achieve notable MP removal efficiency (Table 3), but MPs are still present in DWTP effluents. In addition, household pipes can be made of durable plastic (PVC, PE and fittings of PA), which could deteriorate over time and contribute to the increase in MPs in tap water [21; 171]. However, this contribution from pipes to MP concentration is not always significant and, for example, [PERSON] et al. [168] did not find a difference between MP concentration in the effluent of DWTP and tap water. \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & **(MPs/L)** & **\% MPFs** & **(MPFs/L)** & **References** \\ \hline Brazil & P1: 194 & & & \\  & P2: 438 & - & - & [176] \\ \hline  & 440 a (0–1257) & 74.03 & 5.44 & [21] \\ \cline{2-5}  & P1: 1.6 & & P1: 1.59 & \\ China & P2: 0.9 & 99.2 & P2: 0.89 & [177] \\  & P3: 0.3 & & P3: 0.30 & \\ \cline{2-5}  & 343.5 & 49 & 168.30 & [168] \\ \hline Cuba & 7.17 & 98.3 & 7.05 & [22] \\ \hline Denmark & 0.30 a (0.18–0.6) & 82 & 0.25 & [178] \\ \hline Ecuador & 4.02 & 98.3 & 3.95 & [22] \\ \hline Finland & 47 & 1 & 0.47 & [23] \\ \hline  & 1.82 & 98.3 & 1.79 & [22] \\ \cline{2-5}  & 97 & 8 & 7.76 & [23] \\ \hline  & 0.0007 & - & - & [171] \\ \cline{2-5}  & 53 & 9 & 4.77 & [23] \\ \cline{2-5} Germany & 0 & 0 & 0 & [179] \\ \cline{2-5}  & 0.91 & 98.3 & 0.89 & [22] \\ \hline India & 6.24 & 98.3 & 6.13 & [22] \\ \hline Indonesia & 3.23 & 98.3 & 3.18 & [22] \\ \hline Ireland & 1.83 & 98.3 & 1.80 & [22] \\ \hline Japan & 27 a (7–65) & 17 & 4.59 & [23] \\ \hline Lebanon & 6.64 & 98.3 & 6.53 & [22] \\ \hline Norway & 1 & - & - & [180] \\ \hline Saudi Arabia & P1: 1.9 & - & - & [181] \\ \cline{2-5}  & P2: 4.67 & - & - & [181] \\ \hline Slovakia & 3.83 & 98.3 & 3.76 & [22] \\ \hline Switzerland & 2.74 & 98.3 & 2.69 & [22] \\ \hline Uganda & 3.92 & 98.3 & 3.85 & [22] \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Overview of the incidence of MPs and MPFs in drinking water. “P” followed by a number refers to samples of tap water taken at different points analysed in the cited reference. As can be seen in Table 4, the MP concentration in tap water varies between not detected and 1257 MPs/L, with percentages of microfibres that vary from 1% to 99%, so MPF concentrations are between not detected and 168 MPFs/L, with and average value of 10 MPFs/L. It is noteworthy that, in general, MPFs are the MP form most commonly found in tap water. Regarding MPs analysis in tap water, the procedure is similar to that described for WWTP and DWTP. The most common way to obtain the samples involves a storage container [21, 22, 23, 172, 173, 174, 175, 176, 177, 181] and subsequent filtration or a direct filtration through sieves with different mesh size [171, 178, 179, 180]. In general, samples are oxidized, with H\({}_{2}\)O\({}_{2}\) being the oxidizer agent most frequently used [23]. Nevertheless, some authors employ acids (for example HCl) to degrade organic impurities of the samples [21, 171, 179]. Finally, a visual sorting using the same techniques employed for wastewater samples is carried out [21, 22]. The World Health Organization (WHO) recommended that an adult person should drink 2 L of water per day [182].