Typical Dialysis Water System Requirements
Backflow prevention is incorporated to insure the integrity of a potable water system. In the event a treated water system reverses flow, the backflow preventer will divert the treated water to drain insuring the integrity of the potable water feed. Backflow prevention should be installed to meet state and local requirements.
Temperature Mixing Valve
A temperature mixing valve mixes the cold and hot incoming water feed to approximately 77 degrees F. Advantage – A reverse osmosis membrane is most efficient with a 77 degree F water feed. Disadvantage – Loss of cold or hot water supply pressure will cause the mixing valve to shut off its outlet and consequently shut down the dialysis water purification system.
Water softening, with the use of ion exchange, removes positively charged ions (calcium, magnesium, and heavy metals) from the incoming water supply. The positively charged ions are replaced with sodium ions. The main function of a water softener in a dialysis water purification system is to protect and extend the life of the reverse osmosis membranes. The two styles of water softeners normally used in a dialysis water purification system are: single and duplex softeners.
Carbon filtration is used to remove chlorine, chloramines, and low molecular weight organics through the process of adsorption. Adsorption is the process by which a vapor, dissolved material or very small particle adheres to the surface of a solid. Carbon filtration capacity is commonly sized for the empty bed contact time (EBCT) required to remove chlorine and chloramines from the supply water. AAMI standards for EBCT is 6 minutes for chlorine and 10 minutes for chloramines removal. Carbon beds should be installed in a worker-polisher configuration with test ports installed at the output of both carbon beds. AAMI recommends a test for free and total chlorine is conducted prior to every patient shift.
A reverse osmosis unit used for dialysis should be equipped with the following:
- 5-micron prefiltration
- Pressure readings
- Flow readings
- Temperature monitor
- Conductivity water quality monitor equipped with visual and audible alarms
The distribution system is the piping and valves used to convey the purified water from the water treatment area to the individual dialysis station. Distribution piping is installed in a direct feed or indirect feed style. A direct feed system utilizes the reverse osmosis pump to supply the distribution piping with purified water. An indirect feed system utilizes a storage tank and distribution pump to supply the distribution piping with purified water. Materials that have been used for dialysis water distribution systems include polyvinyl chloride (PVC), natural (non-pigmented) polypropylene, stainless steel and glass. PVC is usually the material of choice for dialysis water distribution systems.
A storage tank should be made of an inert material and be opaque in color. It should be of a sealed-top/coned-bottom design. The tank should also have a hydrophobic vent filter to control airborne bacteria from entering the tank.
Deionization is normally utilized in a dialysis water purification system for the following reasons:
- To provide the best quality water for dialysis
- Emergency bypass in the event of RO failure
- Bacteria control when cation and anion resins are separated
- To polish the reverse osmosis water
- To polish the distribution loop return water before it goes out to the dialysis stations
UV disinfection is utilized in a dialysis water purification system for bacteria control. Final filtration should be utilized at the output of the UV disinfection unit.
Final Filtration of 0.05-micron or smaller is recommended for bacteria and endotoxin control. The final filter or ultrafilter should be the last component the purified wate passes through before going out to the dialysis stations.
The water purification system should be connected to a remote alarm located adjacent to the clinic nurses station. The remote alarm should alarm both audible and visually. The remote alarm should be customized to the water purification system.
The dialysis system monitoring should include a daily check-off sheet, chlorine and chloramines testing, bacteria testing, and endotoxin testing.
Sanitization should be based on bacteria testing and a preventative maintenance schedule. The most common system sanitization chemicals are chlorine and Renalin.