What Water Does a Hospital Use?
A hospital doesn't run on one kind of water. It runs on several, and each department holds its water to a different bar. The sink in a patient room, the final rinse on a surgical instrument, the water feeding a dialysis machine and the makeup water for a boiler usually enter through the same municipal supply. After that, they part ways.
So water treatment for hospitals isn't a single system. It's a set of treatment decisions, one per point of use, each tied to its own standard or guidance document. Get the map wrong and you either over-treat water that never needed it or under-treat the water that touches patients and instruments.
This guide is for the facilities engineer, sterile processing lead or contractor who has to scope that map. It walks through each department, names the document that governs its water, explains what the treatment has to do, and points you to a deeper guide where one exists.
Key Takeaways
Several Waters, Several Rulebooks
ST108 Covers Instrument Water
RO Is Targeted, Not Building-Wide
The Facility Owns Verification
Hospital Water by Department
Start with the whole building on one page. The table below pairs each department with the job its water does, the document that governs it and the treatment function that usually gets it there.
| Where the water is used | What the water has to do | Governing document | Typical treatment function |
|---|---|---|---|
| Building potable water (sinks, showers, ice machines, eyewash stations) | Stay safe to use while limiting growth of Legionella and other waterborne pathogens | CMS memo QSO-17-30, which references ASHRAE Standard 188 and the CDC toolkit; for accredited hospitals, The Joint Commission's water management standard | Water management controls such as temperature management and disinfectant levels, with filtration where the plan calls for it |
| Sterile processing (cleaning, rinsing and sterilizing reusable devices) | Clean without leaving residue, and give a final rinse and steam that don't recontaminate the device | ANSI/AAMI ST108:2023 | Utility water (filtration or softening) for early steps; critical water (RO, DI or distillation) for the final rinse and steam |
| Dialysis | Meet tight chemical, bacterial and endotoxin limits, because the water meets the patient's blood across a membrane | For certified dialysis facilities, the CMS rule at 42 CFR 494.40, which incorporates ANSI/AAMI RD52:2004 | Carbon tanks for chlorine and chloramine, pretreatment, reverse osmosis and a disinfected distribution loop |
| Clinical laboratory | Act as a clean reagent that doesn't skew analyzer results | CLSI GP40 (clinical laboratory reagent water); ASTM D1193 reagent water types for other lab uses | Reverse osmosis followed by deionization polishing |
| Kitchens and ice | Protect equipment from scale and keep taste and clarity consistent | Equipment maker's feedwater requirements; ice machines also sit inside the water management program | Sediment and carbon filtration, plus scale control |
| Boilers, steam plant and cooling towers | Prevent scale and corrosion; cooling towers also carry Legionella risk | Equipment feedwater specs; CMS names cooling towers among the devices that can spread Legionella | Softening, dealkalization or RO for boiler feed; cycles of concentration and blowdown control for towers |
Three kinds of documents sit in that governing column. The CMS memo and 42 CFR 494.40 carry federal weight for facilities that participate in Medicare and Medicaid. The Joint Commission's water management standard applies to the hospitals it accredits. ST108, CLSI GP40 and ASTM D1193 are consensus documents published by AAMI, CLSI and ASTM, which a facility adopts into its own policies and purchasing specs.
Two things stand out once it's laid out this way. First, each document does a different job. The CMS Legionella memo isn't a spec for instrument rinse water, and ST108 isn't a plan for your showerheads. Second, the purest water in the building is produced locally, close to where it's used, not across the whole plumbing system.
Medical Device Processing Water: What ST108 Covers
Sterile processing is easy to under-scope in a hospital water plan, because a Legionella program is built to control pathogen growth in building water, not to define the water quality categories that device processing needs. The document that covers it is ANSI/AAMI ST108:2023. ECRI, the patient safety organization, describes its release as a shift away from advisory best practices for medical device processing water, with a standard that covers water system design, monitoring and maintenance along with steam purity.
Utility water, critical water and steam
ECRI's summary breaks ST108's categories into three, and each one maps to a different step in reprocessing:
- Utility water is tap water, which may need additional treatment. It's used for flushing, washing and the initial rinsing of devices. ECRI gives filtration or softening as examples of bringing municipal water up to this category.
- Critical water goes through extensive treatment to remove microorganisms and contaminants. It's used for the final rinse and to generate steam for sterilization. ECRI names reverse osmosis, deionization or distillation as ways to produce it.
- Steam is the water heated into vapor that sterilizes the devices.
The standard defines parameters such as pH, bacteria, endotoxin and ionic contaminants. The numeric limits live in the standard itself, which AAMI sells, so buy a copy before you set design targets rather than working from a summary, including this one. Poor water quality here isn't cosmetic. ECRI lists corrosion and staining of instruments and a higher risk of microbial transmission among the consequences.
Who monitors it
This is the part that changes how a project gets run. According to ECRI, ST108 requires facilities to set up a multidisciplinary water management team. That team draws on senior leadership, facilities and engineering, infection prevention and device processing staff. Clinical engineering, surgical and procedure room staff and water treatment experts belong on it too.
ECRI adds that under the standard, regular checks are now required rather than just recommended. The responsibility falls primarily on engineering and water maintenance teams, and sterile processing staff need to know what happens when water quality slips.
In practice, that means the equipment conversation and the monitoring conversation should happen at the same table. A critical water system nobody is assigned to test is a system nobody can vouch for.
Building Water and Legionella Control
For the general building supply, the controlling document is a water management program, not a purity specification. The CMS survey memo QSO-17-30 applies to hospitals, critical access hospitals and long-term care facilities, and it says facilities must develop and follow policies and procedures that inhibit microbial growth in building water systems and reduce the risk of Legionella and other opportunistic pathogens. The same memo notes that in a review of US Legionnaires' disease outbreaks from 2000 to 2014, 15 percent were associated with hospitals.
Accredited hospitals have a second rulebook for the same water. The Joint Commission's report on its water management standard says the organization must have a water management program that addresses Legionella and other waterborne pathogens. That program needs an individual or team responsible for it and a basic diagram that maps all water supply sources, treatment systems, processing steps, control measures and end-use points. The team reviews the program annually. It reviews it again when a change to the water system adds risk, or when new equipment or an at-risk water system that could generate aerosols or harbor Legionella is added, including the commissioning of a new wing or building. The standard took effect January 1, 2022, as EC.02.05.02, and the report's November 2025 update lists it as PE.04.01.05 for hospitals and critical access hospitals. Note what it doesn't require: the report states that neither The Joint Commission nor CMS requires culturing for Legionella, and testing protocols are at the hospital's discretion unless law or regulation requires them.
The practical takeaway for treatment is that most of the building's water isn't purified at all. It's managed. CMS gives examples of control measures such as physical controls, temperature management, disinfectant levels, visual inspections and environmental testing for pathogens. Filtration shows up where the program's risk assessment calls for it, and CMS lists water filters among the system components where Legionella can grow, so a filter that isn't maintained becomes part of the risk rather than the fix.
When a program does add treatment equipment, EPA's review of Legionella control technologies for premise plumbing compares the options and says plainly that it isn't recommending any one technology or requiring treatment, so the choice belongs to your risk assessment. For what CMS requires, what it doesn't and how the ASHRAE 188 program elements fit together, see our guide to Legionella water management plans.
Dialysis and Laboratory Water
Dialysis
Dialysis water gets its own rulebook for a simple reason. A person drinking tap water has their gut between the water and their bloodstream. During treatment, a dialysis patient doesn't. The dialysate made from treated water meets their blood across the dialyzer membrane. For certified dialysis facilities, the CMS rule at 42 CFR 494.40 requires water and equipment to meet the water and dialysate quality requirements in ANSI/AAMI RD52:2004, with bacteriological and endotoxin testing at least quarterly. It even sets chlorine and chloramine test triggers at the port after the first carbon tank, with the second tank tested when those triggers are exceeded, which reflects the two-stage carbon design these systems use. A dialysis unit inside a hospital should confirm which set of rules its surveyors apply. The full treatment train, from carbon through reverse osmosis to the distribution loop, is laid out in our guide to water treatment for dialysis.
Clinical laboratory
In the lab, water is a reagent. If it carries ions, organics or bacteria, it can quietly shift analyzer results. Clinical labs work to CLSI GP40's clinical laboratory reagent water, while ASTM D1193 reagent water types cover other lab uses. Reverse osmosis followed by deionization polishing is the usual way to make it, and the grades are compared side by side in our breakdown of laboratory water grades.
Kitchens, Ice Machines, Boilers and Cooling Towers
Kitchens and ice machines
A hospital kitchen looks a lot like any large commercial kitchen when it comes to water. Scale is the main enemy of ice machines, steamers and coffee equipment, and sediment and chlorine taste are the usual complaints. What's different is that ice machines appear on the CMS list of places where Legionella can grow, so filter changes and machine sanitation belong in the water management program's records, not just the kitchen's maintenance log. Sizing and cartridge schedules are covered in the commercial ice machine water filtration guide.
Boilers, steam plant and cooling towers
Central plant water is about protecting equipment. Hardness turns into scale on heat transfer surfaces, and dissolved solids concentrate as water evaporates. Boiler feedwater is usually softened, and sometimes dealkalized or run through RO, depending on pressure and makeup rates. Cooling towers are managed through cycles of concentration and blowdown, and because CMS names them among the devices whose aerosols can transmit Legionella, they belong in the water management program too. The engineering detail is in our guide to boiler feed and cooling tower water treatment.
Do Hospitals Use Reverse Osmosis Water?
Yes, but in specific places rather than everywhere. RO is the workhorse where the water itself has to be very pure:
- Dialysis, where RO is the main purification stage behind carbon and other pretreatment.
- Critical water for device processing, where RO is one of the methods ECRI names, alongside deionization and distillation.
- Laboratory reagent water, where RO is the first stage ahead of deionization polishing.
- Some boiler feedwater, where reducing dissolved solids cuts blowdown and scale.
What RO usually isn't is a whole-building treatment for drinking and handwashing water. The control measures CMS lists for building water, such as temperature management and disinfectant levels, exist to keep pathogens from growing in the pipes, and very pure water at the service entrance doesn't do that job. Purified water gets made locally, distributed carefully and used where its purity matters.
How to Scope a Hospital Water Project
Whether you're adding a sterile processing department, replacing an aging dialysis system or just trying to understand what's already in the basement, the scoping steps are the same.
- List every point of use by department. Walk the building with the table above and note which water class each outlet or machine needs. If you're Joint Commission accredited, start from the water system diagram your water management program already keeps, then add the water class at each end-use point.
- Get a real analysis of the incoming water. Start with your utility's annual water quality report, then test at the building. Ask specifically whether the utility disinfects with chlorine or chloramine. The CMS dialysis rule sets a much lower test trigger for chloramine than for free chlorine, and that difference matters for the carbon design ahead of any RO.
- Assign a target from the governing document. Use ST108 for device processing, the AAMI requirements CMS incorporates for dialysis, CLSI or ASTM grades for the lab and the equipment maker's specs for the central plant.
- Size for peak flow and plan redundancy. A sterile processing department and a dialysis unit can't stop because a membrane or pump is down, so plan redundancy such as duplex treatment trains or standby components. Never plan a bypass that could send untreated water to a dialysis machine, a final rinse or a sterilizer.
- Name who monitors what. Decide which team tests each water class, how often and where the records live, before the system is installed. Then bring the new equipment into the building's water management program review.
No treatment system arrives compliant with ST108 or the AAMI dialysis requirements on its own. Those documents describe water quality and monitoring that the facility has to verify in place, on its own water, with its own testing program. When you talk with a manufacturer, ask what the equipment is designed to produce from your feedwater, and plan your own verification around it.
Crystal Quest® builds equipment for several of these water classes, including the Medical Mid-Flow Reverse Osmosis System, available in capacities from 500 to 7,000 gallons per day, and medical demineralizer (DI) systems for polishing. The right configuration depends on your feedwater analysis, flow and the water class each department needs, which is why a hospital project should start with a conversation rather than a cart.
Planning water for a hospital department?
Send us your water analysis, the departments you're serving and your peak flows, and our commercial team will help you match equipment to each water class.
