## 3 Microplastics and Microfibres in DWTPs  
Drinking water sources are subject to pollution and require appropriate treatment to assure the accomplishment of chemicals standards and the absence of pathogenic agents. Drinking water treatment plants (DWTPs) employ several different water treatment processes to provide safe drinking water for consumers through tap water systems. The most common processes used in these facilities include coagulation-flocculation, followed by sedimentation, filtration and disinfection [160; 161]. The coagulation-flocculation process consists of the addition of chemicals that favour the aggregation of particles that subsequently settle in a clarifier (sedimentation process) [162; 161; 163; 12]. After that, the purification of water continues by means of a filtration process. Pore size and filter material (sand, activated carbon, gravel, etc.) vary depending on the treatment process. Microorganism removal and turbidity reduction occurs during the filtration step [161; 162; 163]. Finally, a disinfection process has to be carried out in order to ensure the absence of pathogenic agents in the drinking water. The disinfecting techniques most frequently employed are chlorination, ozonation and ultraviolet irradiation [164; 165]. MP occurrence in DWTPs has not received as much attention as MPs in WWTPs [164; 165]. However, this is a topic of increasing interest since MPs contained in drinking water could be potentially risky for human health [161; 164; 165; 166]. For example, [PERSON] et al. [33] reported that an American citizen could ingest around 4000 MPs per year by consumption of tap water. Table 3 summarises the incidence of MPs, and particularly microfibres, in DWTPs. As can be observed, there is a wide variety in the concentration MPs, with values that go from absence to 6614 MPs/L in the influent and from absence to 930 MPs/L in the effluent, with an average value of 739 MPFs/L and 236 MPFs/L, respectively. MP concentrations found in influents and effluents of DWTPs are similar or even higher than those reported  
for WWTPs. It must be considered that water for human consumption is exposed to the possible entry of more MPs through several routes, such as environmental degradation of plastics and physical wear of plastic items, industrial discharges, deposition from airborne MPs, etc. [164]. It is remarkable that the abundance of microfibres in most cases is much lower in the influents of DWTPs than those obtained in the influents of WWTPs. This is probably due to the origin of the water--i.e., in DWTPs the influent is obtained from different water sources (aquifers, reservoirs, etc. ), whereas in WWTPs the influents correspond to wastewater (mainly of urban origin) coming from the sewage system. The percentage of MPFs with respect to the total MPs is similar in the DWTP influents and effluents (between 6% and 67%); MPF abundance in DWTP influents is between 0.03 and 176 MPFs/L, with an average value of 110 MPFs/L, whereas in WWTP effluents this average value is 13 MPFs/L. Considering the available data, the removal efficiency of MPFs during the treatment of drinking water is between 25% and 90%. The DWTPs analysed in this work (Table 3) received between 7.8 \(\times\) 10\({}^{6}\) and 5.2 \(\times\) 10\({}^{14}\) MPFs per day, whereas between 1 \(\times\) 10\({}^{8}\) and 7.4 \(\times\) 10\({}^{13}\) MPFs/day are emitted to the environment by DWTP effluent. In general, DWTPs are less efficient in removing MPs and microfibres than WWTPS as a consequence of the usually simpler treatment carried out in the DWTPs [167; 168; 169; 170; 171; 172; 173; 174]. In fact, some WWTPs achieve removal efficiencies above 99%, whereas the highest MPF removal efficiency found in literature for a DWTP was 90.4%, and it was achieved in a DWTP that included coagulation-sedimentation, deep-bed filtration, ozonation and granular activated carbon [171]. Thus, improving MP removal in DWTP is a mandatory issue for the future since this would notably reduce the ingestion of potentially hazardous MPs by humans.