The fluid systems of a dialysis clinic are reviewed from a microbiological standpoint. Water, concentrate and dialysis fluid are the main fluids in the clinic. The quality of these fluids cannot be dealt with, without at the same time reviewing the systems delivering these fluids. The handling of fluids must be seen in a system perspective where every part is important. In the pretreatment of water before reverse osmosis, the incoming water determines the quality. After reverse osmosis,the maintenance in form of disinfection activities is decisive for the microbiological quality in the water system. The dialysis fluid quality is dependent on the water quality as it is produced at the end of the water system. It must be noted that it is not only the number of microorganisms that is of importance but also what the microorganisms do in the fluid systems. Microbiological analysis is not normally able to tell the complete microbiological quality of the fluid systems, as the inner surfaces where the microbial growth takes place are not sent to any laboratory. Consequently, what is seen in samples is only what can come off the surface. The only action that can prevent growth of microorganisms is disinfection but disinfection only is not the solution, it must also be performed regularly. Additionally, all areas of the fluid system must be disinfected. The principle of Quality Assurance including equipment, education and maintenance must be applied in order to ensure microbiological quality.