The origin of this work is the necessity of guaranteeing water quality in underdeveloped countries where the population is supplied with water from rivers, lakes, etc. This water contains a certain number of viruses, bacteria and other microorganisms, which can cause some diseases. In these countries water disinfection methods are not usually applied or cannot be ensured an appropriate effectiveness. On many occasions water is used in the same condition as it is found at the source. This fact causes a high rate of infection that, although not grave in most cases, has been the origin of major epidemics in some circumstances. Membrane technology that allows disinfection on the basis of molecular size of particles is proposed as an option to the current system of treatment. Membrane processes carry out disinfection by means of size exclusion. At the end of the treatment, chlorination at low doses can be a way of keeping water in good condition for long periods of time. The aim of this work is design an ultrafiltration membrane treatment unit, with a spiral configuration, applicable to urban supply systems in underdeveloped countries, which cannot guarantee sufficient water disinfection. The proposed membrane module can be extended to N units, with a consequent increment of treated product, adapting the system to demand. An alternative for the design described has been considered. This option consists of a tubular module of manual operation. This facility intends to provide small communities that are geographically isolated from important urban centres with high-quality water.