Optimizing water consumption in hemodialysis: Key factors and practical strategies

INTRODUCTION

Climate change presents significant challenges across various sectors and is expected to increase the frequency and severity of these problems.^[1] Between 2002 and 2021, droughts affected more than 1.4 billion people. As of 2022, approximately half of the global population experienced severe water scarcity for at least part of the year.^[2] Water scarcity poses a daily challenge for dialysis centers in the most affected regions.^[3] Saudi Arabia, one of the world’s arid countries, faces urgent water resource issues.^[4]

Water scarcity presents serious challenges across multiple sectors, including healthcare. Kidney replacement therapies (KRT) serve as lifesaving treatments for individuals with end-stage kidney disease (ESKD).^[5] More than 850 million worldwide are affected by chronic kidney disease (CKD)^[6], and over 4 million patients globally receive KRT.^[7] Despite advancements in KRT over the past decades, hemodialysis (HD) remains the most widely used technique, accounting for approximately 69% of all KRTs and 89% of all dialysis procedures.^[7] The global dialysis population continues to expand and is projected to reach 5 million next year. The expanding global dialysis population creates a growing environmental footprint. This footprint includes massive water and energy use, significant waste and emissions, and pressures on natural resources, issues that call for innovation, policy action, and broader sustainability integration into healthcare planning.^[8-11]

Modern KRT relies on high-quality medical devices and water purification systems to ensure successful treatment outcomes.^[12] Water consumption in dialysis, particularly in HD, is a major concern due to the large volumes required. The exact amount of water used during dialysis varies, depending on several factors. Approximately 500 L of water is required for each 4 h HD session, with only one-third used for dialysis and two-thirds rejected as reverse osmosis (RO) wastewater is discharged into the drain.^[13] This high water consumption underscores the need for efficient water management systems. Optimizing water use in HD is both a medical necessity and an environmental imperative.

This review explores the current standards and practices for water consumption in dialysis. We discuss multiple strategies and potential solutions to enhance water efficiency, including optimization of RO performance, managing water temperature and quality standards, refining treatment-related consumption calculations, and designing effective water treatment systems in dialysis clinics [Figure 1].

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Figure 1:

Important factors of water consumption in hemodialysis.

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RO SETTINGS: START/STOP TIME

RO has been widely recognized as a safe and effective method of preparing dialysis water since the early 1970s.^[14] Water treatment involves three steps: Pre-treatment, purification, and distribution.^[15] Most RO systems are inefficient, rejecting approximately one-third of the source water at the RO membrane. Different dialysis centers may use varying calculations for setting dialysis start/stop times, depending on factors such as dialysis machine type, self-test duration, patient preparation protocol, nurse-to-patient ratio, connection speed, treatment duration, and adjustment protocols. Machine manufacturers have prioritized reducing preparation and disinfection time while maintaining efficiency and patient safety.

Each day, at startup, an RO system must flush stagnant water from its membranes. The time required for this process is set by the manufacturer based on the duration needed for the conductivity of product water to reach acceptable levels. If hot water circulation occurs overnight, it must be replaced with cold water before dialysis machines begin self-testing for the first treatment.

Modern RO units offer automatic start/stop functionality alongside manual controls. Automated settings reduce staff working hours, minimize patient waiting times, and ensure timely dialysis machine readiness. This automation also benefits post-treatment cleaning and disinfection, as machines and RO systems can be pre-programmed to shut down automatically. Proper RO start/stop time settings are critical for minimizing water consumption. Shorter operation times lead to lower water usage, while unnecessary RO operation increases rejected water volume [Figure 2a and b]. Figure 2a shows 24 h daily RO to supply 2 shifts: The first shift started at 06:00 and the second shift finished approximately at 17:50, the RO unit started automatic or manually but not stopped till the end of the day, the water loss during the period of no dialysis till the end of the day equal to around 14% of total consumption in well-programmed RO. Proper control of the RO unit start and stop times plays a critical role in water conservation, whether the system is operated manually or automatically. Continuous monitoring of dialysis clinic operating hours and regular updates to RO timing settings based on operational feedback are essential to maximize water savings. In other words, any change in dialysis schedules should be reflected in corresponding adjustments to the RO unit’s start and stop times. For example, if the disinfection protocol between treatments or at the end of the day is shortened due to new dialysis machines or manufacturer updates, the overall dialysis day will be reduced. In such cases, the RO stop time can be set earlier to avoid unnecessary operation. The same principle applies to any operational changes that either shorten or extend the day of dialysis; these changes must be considered when programming the RO unit’s start and stop times. Figure 2b shows 24 h programmed RO behavior for 2 shifts, from midnight to 5:50, the unit is in standby mode while heat disinfection for the distribution loop takes place, from 5:50, the RO automatically starts up to supply dialysis machines with water till 17:45, the RO automatically stops producing water and changes mode to standby again. During this day, the total water consumed was approximately.

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Figure 2:

(a) Reverse osmosis (RO) unit showing continuous operation without stop. Temperature in °C of water returned from distribution loop to RO and temperature in hot water tank. Conductivity in μS/cm for inlet water and product water. RO status. (b) RO unit parameters showing auto start and stop. Temperature in °C of water returned from distribution loop to RO and temperature in hot water tank. Conductivity in μS/cm for inlet water and product water. RO status.

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To verify automatic settings, clinic staff and technicians can monitor initial application days and adjust parameters accordingly. Measuring daily water consumption across different shifts and comparing recorded data with expected calculations ensures accuracy. RO remote monitoring provides even more precise verification by tracking actual system start/stop times and assisting in parameter adjustments based on product water volume versus consumption rate.

WATER TEMPERATURE

The required water supply temperature for different dialysis machines is usually in the range between 5 and 30-32°C. The dialysis machine then adjusts the dialysate temperature based on the prescribed settings, which are usually between 36 and 37°C.^[16,17] This temperature is achieved and controlled using internal heaters and temperature sensors inside the dialysis machine. Since dialysis machines do not have cooling systems to lower water temperature, most systems require an inlet temperature close to 32°C. In addition, dialyzer efficiency is often calculated at QD 37°C.

On the other hand, RO membranes function optimally with incoming raw water temperatures between 5°C and 20-25°C. The temperature of the raw water directly impacts both the volume of product water (which increases as temperature rises) and the quality of product water (conductivity increases as temperature increases) [Figure 3a and b]. Figure 3a shows that as the return water temperature value increased above threshold 30-32°C (due to inlet water temperature increased) (time between 14:39-14:56 and 15:01-15:04), the flow rate of consumed water (water consumption) in the RO unit (RO programmed to replace the hot water (higher than threshold) by directing the excess returned water to the drain instate of a feedback to inlet point) increased up to (27 L/m), followed by raw water inlet flow rate increased up to (39 L/m). As soon as the return water temperature value goes below the threshold (14:57-15:00), both flow rates, F5 product water consumption and raw water inlet, decreased. This example shows a direct relationship between the incoming water temperature and water consumption in a dialysis center from one angle, incoming water temperature has another effect on the other hand on product water quality and volume. Figure 3b shows that as the return temperature is below the threshold, both flow rates F5 (consumed product water) and F1 (inlet raw water) are stable and at their minimum (12-15 L/m) and (24-27 L/m), respectively.

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Figure 3:

(a) Water consumption flow affected by increase in temperature. 1- Return temp °C (yellow): Indicating the temperature of the excess product water returned from the clinic distribution loop to the Reverse Osmosis (RO) unit in °C. 2- Flow F5 Cons L/m (brown): Flow rate of consumed product water by dialysis machines connected to the clinic RO distribution loop in liter per minute. 3- Flow F1 inlet L/m: Flow rate of inlet raw water to RO unit in liter per minute. (b) Stable water consumption flow as water temperature is stable and within acceptable range: (Same day time between 12:21 and 12:38) (second shift of a dialysis day) inlet raw water temperature stable below the threshold 1- Return temp °C (yellow): Indicating the temperature of the excess product water returned from the clinic distribution loop to the RO unit in °C. 2- Flow F5 Cons L/m (brown): Flow rate of consumed product water by dialysis machines connected to the clinic RO distribution loop in liter per minute. 3- Flow F1 inlet L/m: Flow rate of inlet raw water to RO unit in liter per minute.

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Thus, controlling incoming water temperature is crucial. Excessively high water temperatures may damage membranes if they are not heat-resistant. In hot countries, raw water temperatures can exceed 45°C during summer, which may facilitate heat disinfection for RO membranes but is unsuitable for normal dialysis operations. Dialysis machines will trigger an alarm and halt dialysate delivery to the dialyzer if the temperature exceeds a certain threshold. Extended exposure to high water temperatures during dialysis can lead to complications such as hemolysis.^[18,19]

For RO systems equipped with heat disinfection, a nonfunctioning cooling system can lead to excess water loss, as the system continually drains hot water to replace it with cooler water. This mimics the startup process post-disinfection but continues indefinitely if the temperature remains above the threshold.

Depending on the geographical location, maintaining proper water temperature is very important. Cold countries may require heating systems, while hot countries generally implement cooling systems to maintain the water temperature as per both dialysis machine and RO incoming water temperature requirements. Cooling systems should be designed based on RO capacity and actual incoming water temperature fluctuations, particularly in summer.

WATER QUALITY

Water quality is critical for safe and effective HD. The composition of incoming water affects dialysis patients’ outcomes.^[20,21] Studies have consistently demonstrated that dialysis quality is directly tied to water purity.^[22] International organizations, including the Association for the Advancement of Medical Instrumentation, the International Standards Organization, and various local organizations, have set standards for dialysis water quality.^[23]

RO manufacturers define specific raw water characteristics necessary for dialysis water production. However, in some regions, raw water quality does not fulfill those required characteristics. Total dissolved solids (TDS) can reach up to 2000 ppm. In such cases, an additional water purification system is needed to meet the required raw water for dialysis.

A pre-RO industrial filtration system (industrial reverse osmosis [IRO]) may be required to process raw water into potable water suitable for dialysis RO filtration. Installing an IRO system is generally more cost-effective than relying on purchased water for dialysis. In addition, an IRO system ensures long-term water quality and sustainability. However, the IRO unit will increase water consumption, as it produces membrane reject water and requires backwashing for its filters. This also increases energy and maintenance costs.

BROKEN PIPES AND WATER LEAKAGE RISKS

Dialysis centers’ RO rooms contain extensive pipe networks connecting various filtration stages before the RO membrane unit. These systems vary across clinics depending on incoming water quality and filtration needs. Some use hoses, while others incorporate fixed piping.

Filters require periodic backwashing, typically conducted during non-dialysis hours, to clean internal filtration materials and maintain functionality. Water leaks can occur due to vibration, temperature fluctuations, high pressure, damaged filters, or pipe failures. If leakage is not detected promptly, significant water loss may occur, especially in setups where booster pumps continuously maintain operational pressure.

To mitigate leakage risks, clinics should implement:

• Water detection systems in RO rooms automatically shut off the water supply if a leak is detected.

• Advanced pressure control mechanisms for booster pumps to help minimize uncontrolled water loss.

• Routine testing and monitoring of detection systems to prevent false alarms and ensure consistent functionality.

DIALYSIS PRESCRIPTION AND WATER CONSUMPTION CALCULATION

Water consumption can be calculated based on dialysate flow rate, time, and disinfection cleaning of the dialysis machine. In dialysis clinics, several additional key factors influence water consumption, primarily related to the water treatment system. These factors vary from clinic to clinic depending on the specific setup, which is itself influenced by water quality, temperature, and the technology used. Important considerations include the volume of rejected water from the RO unit during operation, the methods used for cleaning and disinfecting the RO membrane, and the frequency and type of backwashing for water filters. All of these elements should be taken into account when calculating water consumption per treatment.^[13] Because of these variables, it is challenging to establish fixed consumption values per treatment or a definitive acceptable consumption range. In addition, one more factor to consider in a dialysis clinic is the number of treatments; more treatment means more utilization of produced water.

Modern RO systems incorporate water-saving technologies, allowing unused water to circulate back through the system rather than being discarded. However, periodic RO cleaning and disinfection cycles are unavoidable, meaning higher treatment volumes still lead to increased total water consumption.

WATER CONSUMPTION PER DIALYSIS MODALITY

Basically, HD requires 500 L of water per treatment, and for dialysis prescription of 3 times a week, each dialysis patient uses approximately 80,000 L of water/year.^[24] Hemodiafiltration (HDF), which combines both diffuse and convective, can consume up to 30% more water due to the higher convection volumes needed to achieve targeted adequacy.^[25] Mesic et al.^[26] investigated the effect of automated dialysate flow rate adjustment based on blood flow, aiming to optimize dialysate consumption while preserving or enhancing dialysis adequacy. In a randomized crossover trial conducted across multiple dialysis centers, conventional HD was compared with HDF using an automated Qd:Qb ratio of 1:2. This approach resulted in an 8.5% reduction in dialysate consumption while simultaneously achieving a 3.5% increase in dialysis dose (Kt/V).^[26]

Building on this, Canaud et al.^[27] recently assessed dialysis fluid consumption and efficiency in post-dilution HDF compared with high-flux HD, with the goal of improving resource utilization without compromising efficacy. Conventional high-flux HD typically employs a Qd:Qb ratio of 1.4:1.5, leading to substantial dialysate use averaging ~125 L/session. By optimizing HDF prescription with a reduced Qd:Qb ratio of 1:2, the investigators demonstrated equivalent or superior solute clearance while lowering total dialysis fluid consumption to ~99 L/session, a 26% reduction compared with traditional HDF.

Given the increasing focus on environmental sustainability, dialysis system designs must prioritize water-saving technologies without compromising treatment quality or efficacy.

DESIGN OF WATER TREATMENT SYSTEM IN DIALYSIS

There are many guides and standards on designing water systems for dialysis clinics, focusing primarily on achieving pure water suitable for dialysis treatments by maintaining acceptable ranges of microbiological contamination and chemical composition (acceptable amounts of dissolved solutes in water).^[28-30] Considering water conservation during the design phase can be more efficient and cost-effective than implementing hardware and software water saving techniques later. This can start with installing water measuring devices at different stages of the water treatment system, especially if they are not already built into those stages. These devices help monitor and identify areas of high water consumption, enabling the provision of targeted solutions.

The design should study the locations where to install those volume measuring devices, including the pre-RO units, which may be necessary in areas with high salinity (high amount of dissolved solutes in the water). Pre-treatment filters should also be monitored to identify any unexpected high water consumption. In addition, a water leakage detector should be installed to stop water flow to various components if water is detected on the floor, indicating a broken pipe, overflow, or other faults. Such incidents, if unnoticed, can cause significant water loss and damage to facility components, especially if they occur when the clinic is closed.

Even during dialysis time, water leakage can cause damage to the RO unit components before it is found by the staff. It is clear that type, number of pretreatment filters, and capacity, as well as the RO unit, are calculated and designed based on clinic capacity (number of stations) and quality of incoming water. Expected water consumption can be calculated based on each component’s specifications. For example, pretreatment filter regeneration frequency can be set automatically based on the volume of filtered water and the level of specific components in the incoming water or manually based on expected volumes.

Daily water tests to check the level of some dissolved solutes should take place on a daily basis, as per the majority of guidelines, before the start of treatment (hardness, iron, PH, and TDS) and before each treatment for total chlorine. These tests, along with regular chemistry tests, can indicate changes in incoming water quality and the need to adjust filter regeneration frequency. Assuming pre-treatment filter regeneration consumes 20-30% of total water consumption, monitoring and calculating filter regeneration frequency regularly will contribute to water savings. Online monitoring of hardness and total chlorine levels before and after filters will further enhance the process of monitoring and controlling the filter’s water consumption. By comparing the calculated volume of water from each stage and the consumed product water by dialysis machines to actual consumption measurements, overall and stage-specific performance can be evaluated. This helps identify defects and generate new ideas for water conservation.

CONCLUSION

Dialysis remains a vital treatment for patients with ESKD, yet most HD services continue to consume significant amounts of water. Through a comprehensive analysis of current practices, this review highlights how advancements in technology and optimization of treatment protocols can substantially reduce water consumption while maintaining high standards of patient care. Rigorous monitoring and management of water treatment systems present a valuable opportunity for quality improvement, ensuring more efficient resource use. In addition, educating healthcare professionals and patients on the importance of water conservation in dialysis can foster more responsible and sustainable practices. Dialysis centers can achieve up to 40% water savings by combining optimized dialysate flow, RO reject water reuse, and efficient treatment systems. These measures not only reduce environmental impact but also lower operational costs while maintaining patient safety.

This review underscores the urgent need for the dialysis community to adopt sustainable approaches in response to global water scarcity and climate change. Further research and real-world studies on sustainable dialysis practices should be actively promoted and encouraged, ensuring the future of kidney care aligns with ecological responsibility and patient-centered efficiency.