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ArticleBONENT CHN Exam Guide 2026: Certified Hemodialysis Nurse Prep14 min read

2026 Statistics

Key Facts: CHWS Exam

150

Exam Questions

BONENT CHWS

3 hrs

Exam Time

BONENT

Passing Score (MSPS)

BONENT all exams

20%

Water Purification Equipment

Largest domain

$235–255

Exam Fee (USA)

BONENT 2026

5 + 5 min

Serial Carbon-Bed EBCT

At maximum product-water flow

The CHWS exam contains 150 questions over 3 hours. Water Purification Equipment is the largest domain at 20%, covering RO, pretreatment, deionization, UV, and distribution-loop design. Eligibility requires 1–3 years of dialysis-water experience depending on education or qualifying credentials. BONENT certification demonstrates mastery of ISO 23500-3:2024, the distinct CMS-incorporated AAMI requirements, contaminant hazards, and disinfection practices essential for patient safety.

Sample CHWS Practice Questions

Try these sample questions to test your CHWS exam readiness. Each question includes a detailed explanation. Start the interactive quiz above for the full 100+ question experience with AI tutoring.

1Which federal law establishes maximum contaminant levels (MCLs) for public drinking water supplied to dialysis facilities?

A.Safe Drinking Water Act (SDWA)

B.Clean Water Act (CWA)

C.Resource Conservation and Recovery Act (RCRA)

D.Toxic Substances Control Act (TSCA)

Explanation: The Safe Drinking Water Act (Public Law 93-523) was enacted on December 16, 1974 and authorizes EPA drinking-water standards, including primary maximum contaminant levels. Dialysis facilities receive source water regulated under the SDWA, but facility treatment must then meet the applicable dialysis-water requirements.

2Under CMS Conditions for Coverage for end-stage renal disease (ESRD) facilities, which individual is ultimately responsible for the water treatment program?

A.Clinical Manager

B.Medical Director

C.Biomedical Technician

D.Governing Body

Explanation: CMS ESRD Conditions for Coverage assign the Medical Director ultimate physician-level responsibility for the water treatment program, including policy approval and corrective-action oversight. The biomedical technician performs day-to-day monitoring; the clinical manager oversees nursing operations.

3The FDA classifies dialysis water treatment systems as which device type requiring 510(k) premarket notification?

A.Class I exempt device

B.Class II device

C.Class III device requiring PMA

D.Humanitarian Use Device (HUD)

Explanation: Dialysis water treatment systems are FDA Class II medical devices subject to 510(k) premarket notification, general controls, and special controls. Class II classification reflects moderate risk and substantial equivalence to predicate devices; Class III requires full PMA and applies to high-risk implantable devices.

4Under ISO 23500-3:2024, what is the maximum allowable total viable microbial count in dialysis water?

A.Less than 50 CFU/mL

B.Less than 100 CFU/mL

C.Less than 200 CFU/mL

D.Less than 500 CFU/mL

Explanation: ISO 23500-3:2024 requires the total viable microbial count in dialysis water to be less than 100 CFU/mL. It requires an action level based on the system's microbial dynamics and says that level will typically be 50% of the maximum, or 50 CFU/mL.

5Under ISO 23500-3:2024, what is the maximum allowable endotoxin concentration in dialysis water?

A.Less than 0.125 EU/mL

B.Less than 1 EU/mL

C.Less than 0.25 EU/mL

D.Less than 2 EU/mL

Explanation: ISO 23500-3:2024 requires dialysis-water endotoxin to be less than 0.25 EU/mL. It also requires an action level and says that level is typically set at 50% of the maximum, or 0.125 EU/mL.

6Which current ISO part specifies minimum quality requirements for the dialysis fluid delivered for hemodialysis and related therapies?

A.ISO 23500-5

B.ISO 23500-3

C.ISO 23500-2

D.ISO 9001

Explanation: ISO 23500-5:2024 addresses the quality of dialysis fluid. ISO 23500-3:2024 addresses water used to prepare dialysis fluids; keeping the two parts distinct prevents water limits from being mislabeled as final-dialysis-fluid limits.

7NSF International is involved in dialysis water treatment primarily through:

A.Setting federal MCLs for drinking water contaminants

B.Certifying components to performance standards

C.Requiring 510(k) submissions for RO membranes

D.Issuing interpretive guidelines for CMS V-tags

Explanation: NSF International (National Sanitation Foundation) is a standards development and product-certification organization. NSF/ANSI standards (e.g., NSF 61 for materials in contact with drinking water) certify that plumbing components and water treatment equipment meet performance and safety criteria relevant to dialysis systems.

8Hardness in water is caused primarily by dissolved:

A.Sodium and potassium ions

B.Calcium and magnesium ions

C.Iron and manganese ions

D.Chloride and sulfate ions

Explanation: Water hardness is defined by dissolved calcium (Ca²⁺) and magnesium (Mg²⁺) ions. These divalent cations scale equipment, foul RO membranes, and exhaust water softener resin. Hardness must be removed before water reaches the RO to protect membrane life and product water quality.

9In a conventional sodium-cycle softener regenerated with NaCl, calcium and magnesium are exchanged for:

A.Hydrogen ions (H⁺)

B.Sodium ions (Na⁺)

C.Chloride ions (Cl⁻)

D.Potassium ions (K⁺)

Explanation: Cation exchange resin in a water softener is regenerated with NaCl (brine). Ca²⁺ and Mg²⁺ ions in feed water displace Na⁺ from the resin beads, hardening the resin while releasing sodium into the softened water. Regeneration restores Na⁺ sites by flushing concentrated brine through the resin bed.

10Chloramine (monochloramine) is formed when municipal water plants combine chlorine with:

A.Fluoride

B.Ammonia

C.Bicarbonate

D.Sulfate

Explanation: Monochloramine (NH₂Cl) forms when chlorine reacts with ammonia (NH₃) added by municipal water utilities as a secondary disinfectant. Chloramine is a more stable disinfectant than free chlorine, persists longer in distribution systems, and is more difficult to remove — requiring activated carbon with adequate empty bed contact time.

About the CHWS Exam

The CHWS certification validates specialized expertise in the systems that purify source water before it is used to prepare dialysis fluid. The 150-question, 3-hour exam covers seven domains: Water Quality Standards (15%), Water Treatment Terminology (5%), Basic Water Chemistry (15%), Risks & Hazards of Inadequately Treated Water (15%), Water Purification Equipment (20%), Water System Performance & Monitoring (15%), and Disinfection Strategies (15%). Key technical areas include current ISO and CMS-incorporated water requirements, RO membrane performance, carbon EBCT for chloramine removal, biofilm management, and disinfection verification.

Questions

150 scored questions

Time Limit

3 hours

Passing Score

70 scaled score (MSPS)

Exam Fee

$235–$255 (Board of Nephrology Examiners Nursing and Technology (BONENT))

CHWS Exam Content Outline

20%

Water Purification Equipment

Pretreatment (multimedia, carbon, softener), reverse osmosis (single/double-pass, rejection, recovery), deionization, UV, ultrafiltration, distribution loop design, system design, and vendor selection

15%

Water Quality Standards

SDWA, FDA requirements, ISO 23500-3:2024 chemical and microbiological quality, CMS Conditions for Coverage and incorporated AAMI provisions, and water-quality associations

15%

Basic Water and Water Quality

Water chemistry (pH, ions, hardness, redox), hydrologic cycle, contaminant sources, acids, bases, and fundamental analytical chemistry

15%

Risks & Hazards of Inadequately Treated Water

Chloramine toxicity (hemolysis), aluminum (encephalopathy), fluoride, copper, endotoxin (pyrogenic reactions), microbiological contaminants, source water surveillance

15%

Water System Performance and Monitoring

Microbiological culture methods, LAL endotoxin testing, chloramine (DPD) testing, conductivity, hardness titration, automated/manual monitoring, trending, and system failure investigation

15%

Disinfection Strategies and Prevention Practices

Chemical disinfection (PAA, bleach, formaldehyde, ozone), thermal sanitization, biofilm management, residual testing, high-level disinfection, and outbreak remediation

Water Treatment Terminology and Acronyms

Core industry terminology, units of measure (gpg, EU/mL, CFU/mL, µS/cm), and calculation formulas for EBCT, recovery, rejection, and log reduction

How to Pass the CHWS Exam

What You Need to Know

Passing score: 70 scaled score (MSPS)
Exam length: 150 questions
Time limit: 3 hours
Exam fee: $235–$255

Keys to Passing

Work through all 100 available questions
Review every answer and explanation
Track weak areas and revisit them
Use our AI tutor for tough concepts

CHWS Study Tips from Top Performers

1Keep ISO 23500-3:2024, CMS-incorporated AAMI RD52 requirements, and final-dialysis-fluid limits distinct; always identify the reference before applying a threshold

2For ISO 23500-3:2024 dialysis water, distinguish the <100 CFU/mL and <0.25 EU/mL maxima from system-specific action levels that are typically 50% of maximum

3For chloramine control, each of two serial carbon beds needs at least 5 minutes EBCT at maximum product-water flow, for at least 10 minutes total

4For total chlorine or chloramine, use a permitted sensitive method at the first-bed outlet at the start of the treatment day and before each shift, or about every 4 hours without set shifts

5Understand RO performance: % Rejection = (Feed − Permeate conductivity) / Feed × 100; Recovery = Permeate flow / Feed flow × 100

6Know the clinical toxicity syndromes: chloramine → hemolysis; aluminum → encephalopathy; endotoxin → pyrogenic reactions

7Distribution-loop design should support continuous recirculation, eliminate dead-end piping, and use materials compatible with the selected disinfectants

8UV at 254 nm inactivates microorganisms but does not remove endotoxin; in the purified-water path it needs a downstream endotoxin-reducing means, such as UF or an appropriately located RO

9Know the required monitoring and documentation schedule, including monthly microbiological testing of established systems and chlorine/chloramine logs

10Understand disinfectant residual verification: PAA requires PAA-specific test; bleach requires DPD chlorine test; both must confirm zero residual before patient use

Frequently Asked Questions

What is the CHWS certification?

The CHWS (Certified Hemodialysis Water Specialist) is a BONENT credential for professionals who design, operate, and maintain water-treatment systems in hemodialysis facilities. It validates knowledge of current ISO standards, CMS-incorporated requirements, purification equipment, monitoring methods, and disinfection practices that protect dialysis patients from waterborne contaminants.

How many questions are on the CHWS exam?

The CHWS exam contains 150 multiple-choice questions and has a 3-hour time limit. It is offered in paper-and-pencil format at approved testing sites and as computer-based testing (CBT). The minimum scaled passing score (MSPS) is 70.

What are the CHWS eligibility requirements?

Eligibility requires 3 years of dialysis-water experience with a high-school diploma, 2 years with an associate degree, or 1 year with a bachelor's degree, current qualifying BONENT/NNCO/NNCC certification, or healthcare credential. Two signed and dated reference letters are also required: one from the immediate supervisor and one from a nephrology professional.

What topics are covered on the CHWS exam?

The CHWS exam covers seven domains: Water Quality Standards (15%), Water Treatment Terminology (5%), Basic Water Chemistry (15%), Risks & Hazards of Inadequately Treated Water (15%), Water Purification Equipment (20%), Water System Performance & Monitoring (15%), and Disinfection Strategies (15%). Water Purification Equipment is the largest domain.

How much does the CHWS exam cost?

BONENT exam fees are $235 for paper-and-pencil testing and $255 for computer-based testing in the USA. An optional expedited application fee of $100 is available for faster processing. Annual certification maintenance requires a $65 fee after passing.

Why must CHWS candidates identify the governing water-quality reference?

ISO 23500-3:2024 sets dialysis-water maxima below 100 CFU/mL and 0.25 EU/mL; its action levels are system-based and typically 50% of those maxima, not universal fixed values. U.S. CMS Conditions for Coverage still incorporate older AAMI RD52 provisions: below 200 CFU/mL and 2 EU/mL, with action at 50 CFU/mL and 1 EU/mL. Water and final-dialysis-fluid limits are also distinct.

How should I prepare for the CHWS exam?

Download and study the official BONENT CHWS Study Guide and content outline. Focus on Water Purification Equipment (20%), including RO mechanics, serial carbon-bed contact time, and loop design. Distinguish ISO 23500-3:2024 from CMS-incorporated AAMI requirements, and master monitoring, trend response, and disinfection verification.