A single hemodialysis session uses roughly 357 litres of water, and much of that never even touches a patient’s blood. That figure accounts for the treated water that flows through the dialysis machine plus the water consumed during purification, rinsing, and disinfection. Because most patients on hemodialysis receive three treatments every week, the annual water footprint per person easily climbs past 50,000 litres. Understanding why dialysis demands so much water, and what happens to that water before it reaches the dialyzer, reveals a surprisingly complex process that sits at the intersection of medicine, engineering, and environmental science.
Why Dialysis Needs Water at All
Your kidneys filter your blood continuously, removing waste products and excess fluid at a rate of about 180 litres per day. When kidneys fail, a machine has to take over that filtering job. In hemodialysis, blood is drawn from the body through tubing, passed through a device called a dialyzer (sometimes called an artificial kidney), and returned. Inside the dialyzer, the blood flows on one side of a thin membrane while a specially prepared fluid called dialysate flows on the other side. Small waste molecules like urea and creatinine move from the blood across the membrane into the dialysate, driven by the natural tendency of molecules to travel from areas of high concentration toward areas of low concentration.
This movement, called diffusion, is the primary mechanism of hemodialysis. Small solutes cross the membrane at rates tied to their size and the concentration difference between blood and dialysate.1PubMed Central. Improving Solute Clearances by Hemodialysis At the same time, a pressure difference across the membrane pushes excess fluid out of the blood, a process called ultrafiltration. Larger molecules can be dragged along with that fluid, which helps remove toxins that diffusion alone handles slowly.2PubMed. Basic mechanisms governing solute and fluid transport in hemodialysis In both cases, the dialysate is the vehicle that carries waste away. Fresh dialysate has to flow constantly across the membrane so that the concentration gradient stays steep and waste keeps moving out. Once dialysate has picked up those toxins, it is spent and discarded. This is why dialysis is so water-intensive: the machine needs a continuous supply of clean fluid to keep the gradient working.
How Much Water One Treatment Actually Consumes
A standard hemodialysis session lasts about four hours, with dialysate flowing at a typical rate of 500 millilitres per minute. That alone works out to 120 litres of dialysate over the session. But the total water consumed is much higher. A recent audit of modern hemodialysis systems found that average water consumption was about 357 litres per treatment once you include everything: the dialysate itself, machine priming and rinsing, and the water used to clean and disinfect the system between patients.3PubMed Central. Updating the Data: The Resource Consumption of Modern-Day Hemodialysis Systems
On top of that, the purification process that turns municipal tap water into medical-grade water rejects a large fraction of the incoming supply. Reverse osmosis, the backbone of water treatment in dialysis, works by forcing water through an extremely tight membrane that blocks contaminants. In doing so, up to 60 to 70 percent of the source water is discarded as reject, or concentrate.4Journal of Nephrology. Reuse of dialysis reverse osmosis reject water for aquaponics and horticulture So for every litre of purified water produced, roughly two litres of tap water go in, meaning the true draw from the municipal supply for a single session can exceed 500 litres. Multiply that by three sessions per week for an individual patient, and the numbers grow fast.
Turning Tap Water Into Dialysate
Tap water is safe to drink but far too contaminated for direct contact with your bloodstream. Drinking water standards allow levels of chlorine, fluoride, aluminum, and bacteria that would be dangerous if introduced across a dialysis membrane, where there is no gut lining to act as a barrier. The water treatment process inside a dialysis facility is often called a “water treatment train” because it involves multiple sequential steps, each targeting a different category of contaminant.
The first stages typically involve sediment filtration and water softening to remove particles and calcium or magnesium that could damage downstream equipment. Chlorine and chloramine, which municipalities add to disinfect drinking water, must be stripped out because they can damage red blood cells. The most common method for removing chlorine has been granular activated carbon filters, which adsorb chlorine compounds as water passes through beds of carbon.5PubMed. Dechlorination by ultraviolet radiation: a suitable alternative to activated carbon in dialysis water systems? After dechlorination, the water enters the reverse osmosis unit, which strips out dissolved ions, heavy metals, and organic molecules.
For standard hemodialysis, this purified water is mixed with concentrated electrolyte and buffer solutions inside the dialysis machine to create fresh dialysate on the spot. In more advanced therapies like online hemodiafiltration, some of that fluid is directly infused into the patient’s bloodstream to replace the large volumes of plasma water removed during treatment. That raises the purity bar even further. To achieve the required sterility, ultrapure dialysis fluid is produced by passing standard dialysate through cascades of bacteria- and endotoxin-retentive filters just upstream of the dialyzer.6PubMed Central. Endotoxin-Retentive Filters for the Online Preparation of Ultrapure Dialysis Fluid and Non-Pyrogenic Substitution Fluid This final polishing step is critical because even traces of bacterial fragments can provoke inflammatory reactions when they enter the blood.7PubMed. Microbiological quality and quality control of purified water and ultrapure dialysis fluids for online hemodiafiltration in routine clinical practice
What Happens When the Water Is Not Clean Enough
The consequences of poor water quality in dialysis are not abstract. Patients on hemodialysis are exposed to far more water than anyone who simply drinks from the tap. Over the course of a year, a hemodialysis patient’s blood is exposed to the equivalent of thousands of litres of dialysate. Any contaminant present at even very low concentrations adds up through repeated exposure.
Aluminum is one well-known example. The metal is cleared by healthy kidneys, but in patients with end-stage kidney disease, aluminum can accumulate and cause neurological damage. In low- and middle-income countries, contaminated dialysis water remains a documented source of aluminum toxicity.8Toxicology Reports. A case report of a 79-year-old female with aluminum toxicity presenting with altered mental status in Eldoret, Kenya Historically, recognition that certain clinical symptoms in chronic dialysis patients were linked to fluid quality was what drove the introduction of formal water treatment protocols in the first place.9PubMed. Purification of dialysis fluid: historical background and perspective
Bacteria pose a different but equally serious threat. Even when the dialysate leaving the treatment system meets microbiological standards, biofilms can develop inside the tubing and distribution pipes of the dialysis machine. These slime-like colonies of bacteria adhere to surfaces, resist routine disinfection, and periodically shed bacteria and endotoxins back into the fluid pathway. Studies have found bacterial counts ranging from roughly a thousand to a million organisms per square centimetre on tubing surfaces inside dialysis systems, along with measurable endotoxin levels.10PubMed. Evidence of bacterial biofilm in tubing from hydraulic pathway of hemodialysis system Stagnation and warm temperatures inside the machine promote this growth, and even a dialysate that tests endotoxin-free at the point of sampling may carry contamination downstream from established biofilm.11PubMed Central. Potentially pathogenic culturable bacteria in hemodialysis waters
When biofilm fragments reach the patient, the consequences range from chronic low-grade inflammation to acute bloodstream infections and sepsis.12PubMed. Biofilms and infection in dialysis patients This is why dialysis centres invest heavily in cleaning protocols, heat disinfection cycles, and routine water testing. Water quality is not a one-time engineering problem; it requires continuous monitoring.
Home Hemodialysis and the Water Bill
Dialysis does not have to happen in a clinic. A growing number of patients perform hemodialysis at home, which offers scheduling flexibility and, in some studies, better clinical outcomes. But moving the treatment home means the patient absorbs the utility costs that a hospital or clinic would otherwise cover.
A Canadian simulation estimated the annual utility cost of home hemodialysis at anywhere from about $420 to roughly $1,270 per year, depending on the prescription. Patients who dialyse more frequently or for longer sessions, such as nocturnal hemodialysis six nights a week, sit at the high end. Water consumption accounted for the overwhelming majority of that expense, with electricity making up only about 12 percent of the total.13PubMed Central. Estimating patient-borne water and electricity costs in home hemodialysis: a simulation For patients already dealing with the financial strain of chronic illness, that cost transfer is significant and not always well communicated ahead of time.
Machine design has been evolving in response. Newer home hemodialysis machines place greater emphasis on water conservation and simplified water purification setups, reducing both the infrastructure burden and the overall water footprint compared to older clinical systems.14Nature Reviews Nephrology. Water quality in conventional and home haemodialysis Some systems use smaller volumes of dialysate or incorporate partial recycling, which brings down the total water use per session without necessarily sacrificing waste clearance.
The Environmental Footprint of Dialysis Water Use
Globally, well over two million people receive hemodialysis. When you multiply the water demands of each treatment by three sessions a week across that population, the environmental impact is substantial. Dialysis centres are among the most water-intensive settings in healthcare, and the energy required to heat, purify, and pump that water adds a meaningful carbon footprint on top of the raw consumption. A Japanese hemodialysis clinic that formed a dedicated resource-saving committee found that utilities, including water, gas, and electricity, represented a major portion of its operational expenses.15Frontiers in Health Services. Economic and environmental impacts of a resource-saving committee in a Japanese hemodialysis clinic: a case study
The reject water from reverse osmosis is a particularly frustrating source of waste. That 60 to 70 percent of incoming water that gets discarded during purification is not actually dirty; it is just more concentrated in dissolved minerals than what passes through the membrane. It is perfectly usable for many non-medical purposes, yet in most facilities it flows straight down the drain.
Strategies for Reducing Dialysis Water Waste
Efforts to make dialysis more water-efficient generally fall into three categories: reducing the amount of water used per treatment, reusing the reject water for other purposes, and developing technologies that recycle dialysate.
On the “reduce” front, one straightforward approach is lowering the dialysate flow rate. A standard rate is 500 millilitres per minute, but a study comparing that to a reduced rate of 400 millilitres per minute during expanded hemodialysis found no significant difference in the clearance of medium-sized waste molecules. The lower flow rate saved an average of 24 litres of water per patient per session, which added up to nearly 14,000 litres over just 12 weeks in that study cohort.16PubMed Central. Toward Green Dialysis: Efficacy and Sustainability with Reduced Dialysate Flow in Expanded Hemodialysis If widely adopted, even modest per-session savings like this would translate to enormous aggregate reductions.
Reusing reverse osmosis reject water is probably the lowest-hanging fruit. Because this water is simply mineral-rich rather than hazardous, it can be redirected to gardening, aquaponics, toilet flushing, or even hospital sterilization processes.17PubMed Central. Hemodialysis water reuse within a circular economy approach. What can we add to current knowledge? A point of view. A Sydney hospital implemented a system to capture reject water from its 17-station hemodialysis service and documented meaningful annual savings in both water costs and carbon emissions.18PubMed Central. Reusing Haemodialysis Reverse Osmosis Reject Water: A Case Report From a Sydney Metropolitan Hospital, Australia Other groups have tested using reject water for aquaponics and horticulture with encouraging results.4Journal of Nephrology. Reuse of dialysis reverse osmosis reject water for aquaponics and horticulture These reuse strategies align with a broader “circular water management” framework proposed in the nephrology literature, which adapts the classic reduce-reuse-recycle model specifically for dialysis.19PubMed. Water implications in dialysis therapy, threats and opportunities to reduce water consumption: a call for the planet
Despite their promise, reject water reuse programs face practical hurdles. Plumbing modifications are needed to capture and redirect the water. Regulatory frameworks vary by region, and some building codes do not easily accommodate non-potable water reuse. Hospital administrators may view the up-front infrastructure investment as hard to justify even when the long-term savings are clear. As a result, adoption remains patchy even in countries where water scarcity makes the case obvious.
Sorbent Technology and the Future of Water-Light Dialysis
The most radical approach to cutting water use in dialysis involves not producing fresh dialysate at all but instead cleaning and recycling the same small batch of dialysate throughout a session. This is the idea behind sorbent-based dialysis. Sorbent cartridges contain materials that selectively bind and remove the uremic toxins that accumulate in used dialysate, regenerating the fluid so it can pass through the dialyzer again. If perfected, this approach could shrink the water requirement from hundreds of litres down to just a few.
Sorbent systems are not new — they were used in portable dialysis machines decades ago — but a modern revival is underway. Current interest is driven partly by the environmental case for reducing water use during conventional dialysis and partly by the engineering challenge of building portable or wearable artificial kidneys.20PubMed Central. The Revival of Sorbents in Chronic Dialysis Treatment A portable or wearable dialysis device cannot be tethered to a municipal water supply and a drain. It has to work with a small, self-contained volume of fluid that gets continuously regenerated. Dialysate recycling systems based on sorbents are considered among the most promising avenues for making that possible.21Nature Reviews Nephrology. Portable, wearable and implantable artificial kidney systems: needs, opportunities and challenges
The challenges are real, though. Sorbent cartridges need to handle a wide range of solutes, manage acid-base balance, and avoid releasing harmful byproducts as they become saturated. Current cartridges are bulky relative to the small form factor a wearable device demands, and their capacity limits how long a single treatment session can run before the cartridge is exhausted. Several companies and academic groups are working on next-generation sorbent materials, but as of now, no widely available wearable artificial kidney has reached routine clinical use. The technology remains in active development rather than mainstream practice.
Peritoneal Dialysis and Water Differences
Not all dialysis involves a machine and an external blood circuit. In peritoneal dialysis, the patient’s own abdominal membrane serves as the dialysis membrane. A sterile solution is infused into the abdominal cavity through a permanent catheter, wastes diffuse from the blood vessels lining the peritoneum into the solution, and then the fluid is drained out. This modality uses pre-manufactured bags of sterile dialysate rather than water purified on-site, so the direct water footprint at the point of care is much smaller than hemodialysis. There is no reverse osmosis system, no reject water, and no need for a water treatment train in the patient’s home.
That does not mean peritoneal dialysis is water-free, of course. Manufacturing the sterile solution bags at the factory still uses water and energy, and the plastic packaging creates its own waste stream. But from the patient’s perspective, the water utility bill is barely affected, which is a notable contrast to home hemodialysis. The trade-offs between the two modalities are complex and go well beyond water use, involving differences in clinical suitability, infection risk, lifestyle, and long-term outcomes. Still, for patients in water-scarce regions or those concerned about the environmental footprint of their treatment, the lower on-site water demand of peritoneal dialysis is a genuine practical advantage.
Water Scarcity and Global Access
The water intensity of hemodialysis poses an acute challenge in regions where clean water is already limited. In parts of sub-Saharan Africa, South Asia, and the Middle East, municipal water supplies may be unreliable, and the infrastructure to purify water to dialysis-grade standards is expensive to build and maintain. Even where hemodialysis is technically available, the cost of water treatment and the sheer volume of water needed can limit how many patients a centre can treat. Some facilities in low-resource settings operate with suboptimal water quality, which is part of why contamination-related complications like aluminum toxicity continue to be reported in those regions.
Climate change is making this harder. As droughts become more frequent and aquifers are depleted, the tension between medical water needs and agricultural or domestic water needs grows sharper. A dialysis centre in a drought-affected area cannot simply reduce its water use without compromising treatment quality. This is why the push for more water-efficient technologies, reject water reuse, sorbent-based dialysate regeneration, and peritoneal dialysis where clinically appropriate, is not just an environmental talking point. For a growing number of patients around the world, it is a question of whether adequate treatment remains available at all.