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General information about dialysis facility water systems, not medical advice and not a procedure guide.
Short answer
In a dialysis facility, reverse osmosis (RO) is one stage of a longer water treatment system, not the whole system. RO sits after pretreatment (including a component that removes chlorine and chloramine) and before distribution to the machines. The federal rule, 42 CFR 494.40, names the dialysate water standard and the chlorine/chloramine removal component; the section’s text does not use the words “reverse osmosis”.
Definition and scope
Dialysis water treatment is the chain of equipment that turns facility tap water into water fit for making dialysate. Reverse osmosis is the membrane step in that chain: per Kasparek and Rodriguez (2015), an RO unit is “a self-contained unit that uses a high-pressure pump and a semipermeable membrane” that blocks most dissolved ions, organics, bacteria and endotoxin. It is judged by percent rejection (the article gives a target above 90%) and by the conductivity of the product water.
This page covers the water side only. For the machine that uses the treated water, see what a dialysis machine is, and for the fluid it makes, dialysate flow rate.
How dialysis water treatment is put together
Kasparek and Rodriguez list the pretreatment steps that come before the RO membrane: temperature adjustment, backflow prevention, pressurization, sediment filtration, softening and carbon filtration. A secondary carbon tank acts as a backup, and total chlorine is tested frequently. 42 CFR 494.40(b) requires the water treatment system to include a component or carbon tank that removes chlorine/chloramine, with a backup component or second carbon tank in series. The second component is tested when results from the initial one exceed the rule’s chlorine or chloramine limits. If the last component exceeds those limits, the facility must take immediate corrective action or stop treatment, and notify the medical director.
AAMI RD52 versus the ISO-based limits
42 CFR 494.40(a) requires water and equipment to meet AAMI RD52:2004, incorporated by reference. Later documents set tighter water limits. The table below is taken from Table 2 of Kasparek and Rodriguez (Clin J Am Soc Nephrol 2015;10(6):1061-1071) and reflects that article’s date; check the current eCFR text for the standard CMS cites today.
| Document | Bacteria in water | Endotoxin in water |
|---|---|---|
| AAMI RD52:2004 (the standard CMS cited) | below 200 CFU/ml | below 2 EU/ml |
| AAMI/ISO 13959:2009, 23500:2011, RD23500:2014 | below 100 CFU/ml | below 0.25 EU/ml |
What 42 CFR 494.40 requires
- (a) Water and equipment meet AAMI RD52:2004.
- (b) A component or carbon tank removes chlorine/chloramine, with a backup in series; the second component or tank is tested when the first exceeds the rule’s limits; out-of-limit results trigger corrective action or stopping treatment.
- (c) Chemical, microbial and endotoxin results that reach AAMI action levels require a corrective action plan.
- (e) For a preconfigured FDA-approved hemodialysis system, follow the manufacturer’s labeling, meet RD52, and test bacteriology and endotoxin at least quarterly or more often as needed.
CMS Survey and Certification Letter 15-44-ESRD (posted June 26, 2015) states that portable RO units that meet the AAMI water quality standards incorporated at 494.40 may be used in outpatient dialysis facilities.
Checklist of records and documents to ask for
These items map one-to-one to the regulation paragraphs above; they are a way to organize a records review, not a purchasing recommendation.
- Documentation showing the water meets AAMI RD52:2004 (494.40(a)).
- The chlorine/chloramine removal component or carbon tank, and records of testing the second component or tank (494.40(b)).
- The written corrective action plan and records of any action taken on out-of-limit chemical, microbial or endotoxin results (494.40(b), (c)).
- Bacteriological and endotoxin test records, at least quarterly for a preconfigured FDA-approved system, plus the manufacturer’s labeling for that system (494.40(e)).
- For a portable RO unit, evidence that it meets the AAMI water quality standards (CMS letter 15-44-ESRD).
Common misunderstandings
- “RO is the whole treatment.” It is one stage; carbon filtration and the other pretreatment steps come first.
- “The CFR requires reverse osmosis.” Section 494.40 speaks of a water treatment system and a chlorine/chloramine removal component; it does not name RO.
- “Dialysis RO water is lab water.” Dialysis water is judged against dialysis standards. Laboratory grades are a separate system; see laboratory water grades and the laboratory water purification system comparison.
Where it matters for supply decisions
Water records are part of how a unit documents compliance, alongside consumables and equipment. See the outpatient dialysis center supply checklist and the hemodialysis home training supply checklist for the supply side.
FAQ
What is dialysis water treatment?
It is the pretreatment, reverse osmosis and distribution equipment that prepares water for dialysate, held to the standard incorporated in 42 CFR 494.40.
Is RO water the same as laboratory water?
No. Dialysis water is measured against dialysis water standards such as AAMI RD52; laboratory grades follow their own specifications.
How often is water tested?
For a preconfigured FDA-approved hemodialysis system, 494.40(e) calls for bacteriological and endotoxin testing at least quarterly or more often as needed. Other systems follow the monitoring in the facility’s own plan and AAMI action levels.
Who acts when a result is out of limits?
Under 494.40(b), the facility takes immediate corrective action or stops treatment and notifies the medical director.
Sources
- 42 CFR 494.40, Water and dialysate quality, eCFR: ecfr.gov (checked 2026-11-01).
- CMS Survey and Certification Letter 15-44-ESRD, June 26, 2015: cms.gov (checked 2026-11-01).
- Kasparek T, Rodriguez OE. What Medical Directors Need to Know about Dialysis Facility Water Management. Clin J Am Soc Nephrol 2015;10(6):1061-1071: PMC4455220 (checked 2026-11-01).
