The quality of dialysis water

Every week, haemodialysis patients are exposed to approximately 400 l of water used for the production of dialysis fluids which, albeit with the interposition of a semi-permeable artificial membrane, come into direct contact with the bloodstream. It is therefore clearly important to know and monitor the chemical and microbiological purity of dialysis water.

In this review, we analyse the sources of chemical and microbiological water contamination, and the problems involved in water purification systems and modalities. We also analyse the compliance of dialysis units with the microbiological standards established by the most widely accepted guidelines relating to the quality of dialysis fluids.

The risk of chemical contamination is due mainly to the primary pollution of municipal water, whereas the most important microbiological problem is the control of bacterial growth in the water treatment and distribution system. Dialysis water treatment implies various levels of pre-treatment, a final purification module (which, in many cases, is reverse osmosis: RO) and a hydraulic circuit for the distribution of the purified water. RO-based treatment systems produce water of optimal chemical and microbial quality, and so dialysis units need to concentrate on maintaining this quality level in the long term by means of effective maintenance and disinfection strategies. The most widely accepted standards for water purity are those recommended by the Association for the Advancement of Medical Instrumentation and the European Pharmacopea, which respectively allow bacterial growth of <200 and <100 c.f.u./ml, and an endotoxin concentration of <2 and <0.25 IU/ml. However, a number of multicentre studies have reported that 7-35% of water samples have bacterial growth of >200 c.f.u./ml, and up to 44% have endotoxin levels of >5 IU/ml.

The results of multicentre studies indicate that the microbial quality of dialysis fluids is still a too often neglected problem, particularly as there is evidence of a possible relationship between dialysis fluid contamination and long-term morbidity. The time has now come to take advantage of innovations in water treatment processes and improvements in dialysis machines in order to modify clinical practices and start improvement processes aimed at decreasing the risk of microbial contamination to the minimum, as it has already been successfully done in the case of chemical contamination.