All dialysis facilities require a properly designed and maintained water treatment system to safeguard patients. No municipal water can be considered safe for use in hemodialysis applications, in the absence of a treatment system, some of the most toxic contaminants arise from municipal water treatment practices. The core purification process required for producing purified water for renal dialysis is reverse osmosis (RO). Typically, single pass RO plant will meet the microbiological and mineral standards for HD. For haemodiafiltration (HDF), single pass RO systems cannot always be guaranteed to meet the more stringent microbiological standards; as a result, either double pass RO with additional ultrafiltration or sub-micron filtration should be considered when designing water treatment systems for HDF.