In many areas of underdeveloped countries population is supplied with water from rivers, lakes, etc., without applying any water treatment in most cases this water contains a certain amount of virus, bacteria and other microorganisms, which can cause several diseases. The research group of the Chemical and Nuclear Engineering Department of the Polytechnic University of Valencia (Spain) is working in the project: Design and Construction of a Water Potabilization Membrane Facility and its Application to the Third World Countries (AQUAPOT) in collaboration with the non-governmental organization Association for the Cooperation with Ecuador (ACOEC). In this project, membrane technology is proposed as an option to the current system of treatment. The object of the AQUAPOT project is the design and construction of an ultrafiltration membrane treatment unit, with spiral configuration, applicable to urban supplying systems in underdeveloped countries, which cannot guarantee an accurate disinfection of water. Before being placed definitively in Ecuador, the ultrafiltration facility has to be tested in order to prove its right operation. For so, an ultrafiltration unit similar to the one that is being constructed for being applied in Ecuador has been tested with water in much worse microbiological conditions than the water of Ecuador. The aim of this work is to describe these preliminary tests and analyze the ultrafiltration facility performance.