The present thesis, carried out in the framework of the UFTEC project, reports on the results obtained from the comparative operation of four reverse osmosis (RO) experimental units fed by pretreated water coming from the conventional pretreatment or, alternatively, from different ultrafiltration (UF) units. The conventional water treatment studied was the existing one in drinking water treatment plant (DWTP) in Sant Joan Despí (SJD), which consists of dioxiclorination, coagulation/flocculation, settling, and sand filtration steps, while the three UF technologies studied in the project were in-out pressurized UF, out-in pressurized UF, out-in submerged UF. The overall objective of the UFTEC project is to demonstrate the feasibility and the economic viability of direct ultrafiltration (UF) pretreatment for reverse osmosis (RO) as an alternative to the conventional pretreatment such as the one in SJD. The proposed alternative technology should enable reducing economic costs and the environmental impact related to chemicals and energy consumption as well as the water losses in conventional pretreatment for RO. During this three-year long project, the river direct-UF pilot plants have been built, assembled to the RO units, operated and monitored for the evaluation of their performances from a hydraulic and produced water quality perspectives. The impact on RO membranes of the permeate produced by different UF prototypes and the conventional pre-treated water was assessed by evaluating the hydraulic response of the prototype as well as through the autopsy of the RO modules used. Results obtained from the thesis showed that UF technology can indeed be a promising alternative to the conventional treatment as a pretratment previous to a RO unit, especially when facing high turbidity ranges of surface water. Besides providing higher quality water, UF also maintains more stable operation and consumes less chemical reagents. Among the disadvantages are the higher energy consumption and design costs compared to the conventional treatment.