Hemodialysis Water Treatment Systems

Why Water Quality Matters

A healthy person drinks roughly 2 liters of water a day, with the gut and liver acting as barriers before anything reaches the bloodstream. A hemodialysis patient is exposed to a far larger volume under far more dangerous conditions: each session uses roughly 120 to 200 liters of water to make dialysate, separated from the patient's blood only by the thin, highly permeable dialyzer membrane. A patient on thrice-weekly dialysis is exposed to 18,000–30,000 liters of water per year with no gut or liver barrier in between — any contaminant in the water can diffuse directly into the blood.

What contaminated water does to patients

Regulatory and Standards Framework

Two layers govern dialysis water in the Philippines: the international quality standards that define the numbers, and the DOH administrative orders that make compliance a legal condition of your License to Operate (LTO).

2.1 Philippine DOH requirements

2.2 AAMI / ISO 23500 series

The current ISO 23500 series consolidates earlier standalone standards into one framework: water for hemodialysis (formerly ISO 13959), concentrates (formerly ISO 13958), and dialysis fluid quality (formerly ISO 11663). The numeric limits in §7 of this guide trace directly to this lineage and carry forward into current editions. The parts most relevant to the water room are general requirements (Part 1), water treatment equipment (Part 2), water for hemodialysis (Part 3), concentrates (Part 4), and dialysis fluid quality including ultrapure and online fluids (Part 5).

System Design and How It Flows

A dialysis water system is a chain of barriers. Each stage removes a specific class of contaminant and protects the stage that follows. Water always moves in one direction: from the feed source, through progressive purification, into a recirculating loop that feeds the machines, and back.

3.1 Pre-treatment

Pre-treatment conditions raw water so the RO membrane survives. It is the part of the system that fails most often because it does the dirtiest work.

• Sediment / multimedia filter: backwashes periodically (timer-controlled) to flush trapped solids. Watch the pressure drop across it.
• Softener: resin beads swap hardness ions (Ca²⁺, Mg²⁺) for sodium. Requires a brine (salt) tank — never let it run empty.
• Carbon tanks: granular activated carbon adsorbs chlorine and — far more slowly and importantly — chloramine. Two tanks in series ("worker" and "polisher") guarantee breakthrough protection. Empty Bed Contact Time (EBCT) must be adequate (commonly ≥6 minutes total across the tanks at design flow).

3.2 Reverse osmosis (RO)

RO is the core purification step. A high-pressure pump forces feed water against a semipermeable membrane; purified "permeate" (product water) passes through, while concentrated "reject" carries away rejected salts, bacteria, and endotoxin to drain. It removes 90–99%+ of dissolved ions and essentially all bacteria and endotoxin when intact. Key live readings: product (permeate) conductivity or resistivity, percent rejection, feed/reject/permeate pressures, and recovery ratio.

3.3 Storage and distribution loop

Product water is fed directly to the loop or held in a storage tank, then circulated continuously to every machine and back. The enemy here is stagnation, because standing water grows biofilm — a bacterial layer that sheds endotoxin and resists disinfection. Loop design favors continuous recirculation with high flow/turbulence and no "dead legs" (capped, unused pipe stubs where water sits). A vented storage tank uses a hydrophobic 0.2 µm air vent filter and a conical/sloped base for full drainage.

3.4 Ultrafiltration (UF) and polishing

UF membranes (pore size <0.01 µm) sit after RO — often one at the loop and a second point-of-use (POU) UF on each machine — as the final barrier against bacteria and endotoxin. DOH AO 2013-0003 specifically calls for UF after RO for microbial and endotoxin control, and UF is what allows a center to reach ultrapure water for online HDF.

Designing for Your Source Water

The baseline treatment train above assumes a municipal feed. Pre-treatment design must change for deep-well, brackish, and high-hardness sources — these are common variants for provincial and coastal Philippine dialysis centers.

4.1 Municipal / treated water supply (baseline)

The utility has already disinfected — chlorinated or chloraminated — the supply, so the entire pretreatment train downstream of the carbon stage exists largely to undo that disinfection before it reaches the RO membrane and the dialysate. The dual GAC (granular activated carbon) tanks in series specifically guard against chloramine breakthrough: total chlorine is sampled between the two tanks and after the second tank before each shift, with an action limit of ≤0.1 mg/L before treatment may proceed. Utility-side "shock" hyperchlorination events — common after typhoons or flooding, when water districts spike chlorine dosing — are a known precipitant of breakthrough and should be flagged to staff whenever the water district advises one.

4.2 Deep well / borehole / artesian water

Common for provincial centers without a reliable utility connection. The source arrives untreated and biologically/chemically unpredictable, so pretreatment adds steps the municipal train doesn't need — while the dual-carbon chloramine logic above becomes largely irrelevant unless the facility chlorinates the well water itself for storage-tank disinfection.

• Iron and manganese removal: groundwater frequently carries dissolved iron and manganese that precipitate (rust-colored, then black-brown staining) once exposed to air, fouling softener resin, carbon media, and RO membranes if not removed first. Standard approaches are aeration or chemical oxidation followed by filtration, or a manganese greensand filter.
• Higher, more variable turbidity: borehole silt/sand fines argue for a more conservative, often backwashing, multimedia prefilter ahead of the cartridge stage.
• Higher pre-treatment bacteriological risk: with no upstream disinfectant residual suppressing growth in storage cisterns, periodic well-water/storage-tank disinfection and more frequent bacteriology/endotoxin testing of pretreatment-stage water are warranted.
• Baseline contaminant testing: iron, manganese, and hardness are the most commonly reported groundwater issues nationally and should be assumed present until tested. Arsenic is a documented but geographically localized concern in specific Philippine groundwater sources — not an established nationwide hazard — so facility-specific source-water testing (including arsenic) before commissioning a deep-well-fed WTS is the correct practice, not a blanket assumption either way.

4.3 Brackish or saline-influenced water

Coastal and island centers, some within seawater-intrusion range of shallow coastal aquifers, face elevated TDS/conductivity as the dominant design driver rather than organic or microbial load.

The operational trade-off to flag for planning: higher reject (concentrate) volume and lower recovery compared to a freshwater feed mean more feed water consumed per liter of usable permeate — a real cost and logistics consideration (water trucking, cistern sizing, reject disposal) for small coastal/island facilities that already pay a premium for source water.

4.4 Hard water (high calcium / magnesium)

Routine hardness is the softener stage's job, and most limestone-aquifer groundwater sits comfortably within a correctly sized softener's capacity. The design question is what changes at high hardness loads, not whether softening is needed at all.

As source hardness rises, daily grain load (volume treated × grains hardness per gallon) rises proportionally, so an undersized softener exhausts mid-shift or "channels" — hardness breaks through before scheduled regeneration. This is a silent failure mode: the water still looks and tastes normal. Verify post-softener hardness directly rather than assuming the softener is adequate from source hardness alone. Inadequate softening lets calcium and magnesium concentrate at the RO membrane surface, precipitating as calcium carbonate scale that fouls the membrane and shortens its service life — making softener sizing a direct RO-membrane-longevity issue.

Sizing & Capacity Planning

The medical director and facility leadership are responsible for ensuring the WTS can reliably supply every station it serves — undersizing is a documented, recurring cause of clinic-level water-quality failure (Kasparek & Rodriguez, 2015).

5.1 How to measure WTS capacity

1. Capacity is the RO unit's rated permeate (product water) output — liters per hour (LPH) or gallons per day (GPD) — measured at a standard feed temperature (usually 25°C). RO output drops as feed water gets colder (roughly 2–3% per °C below the rating point), so a unit rated at 25°C under-produces on a cool morning unless margin is built in.
2. Calculate actual peak demand, not average usage. Standard single-pass HD draws roughly 500–800 mL/min dialysate flow (≈30–48 L/hr per station); online HDF substitution fluid pushes a station to ~50–60 L/hr. Peak simultaneous demand = (number of stations running at the same time, not total stations in the building) × per-station flow, plus a design margin of 20–30% for recirculation-loop losses and headroom.
3. Compare peak demand against the RO's rated permeate output — not the storage tank size. A large tank can mask an undersized RO for a while, but once the tank draws down faster than the RO refills it, every additional station drops outlet pressure/flow for everyone on the loop.
4. Check the loop, not just the RO. Distribution-loop pipe diameter and recirculation pump must maintain adequate linear velocity — no dead legs, continuous turbulent flow — even after new machine take-off points are added.

5.2 Increasing capacity when machines are added

1. Recalculate total peak demand with the new station count, then size the gap against current RO rated output (with margin) before adding machines, not after.
2. Add a parallel RO skid sized for the increment, rather than replacing the existing unit — this gives N+1 redundancy (one unit can be serviced or fail without losing all capacity).
3. Scale pretreatment with the RO, not just the RO itself. Pushing more flow through the same carbon tanks reduces Empty Bed Contact Time (EBCT), risking chloramine breakthrough. Adding RO capacity without adding matching softener/carbon capacity is a common, dangerous shortcut.
4. Re-size storage and the recirculation loop — bigger or additional storage if peak buffering is needed, and confirm the loop pump and pipe diameter still hit target velocity with the new branch takeoffs.
5. Re-validate and re-document before going live: re-test conductivity/rejection, chlorine, and microbiological/endotoxin counts on the expanded system, and update the facility's Water Quality Management Program (DOH AO 2013-0003) to reflect the new configuration before the added stations treat patients.

Facility Layout & Special Configurations

6.1 Isolation bay placement — hepatitis B and C

Bloodborne pathogens (HBV, HCV, HIV) are not transmitted through the RO-treated water/dialysate supply. Isolation requirements are about dedicated machines, supplies, and physical space — not a separate water-treatment stream. The WTS loop continues to serve every station, isolation included, from one centrally treated supply.

• Hepatitis B surface antigen (HBsAg) positive: current guidance recommends use of a dedicated dialysis machine that is never used for another patient (Jardine et al., 2019), consistent with a separate room and dedicated supply cart given how readily HBV persists on environmental surfaces.
• Hepatitis C positive: a dedicated machine is not required provided strict inter-patient cleaning and disinfection protocols are followed (Martin et al., 2022) — standard precautions plus routine surface/external disinfection on a shared machine is considered adequate. Some facilities still cohort HCV-positive patients by shift as an added margin; this is a facility policy choice, not a water-system requirement.
• Loop/plumbing placement: the isolation room's water/dialysate takeoff is just another branch off the same continuously recirculating loop. The practical engineering concern is that an isolation bay typically runs fewer patients per week, so its branch is more prone to becoming a low-flow dead leg that breeds biofilm. Keep the branch as short as possible, site the room where its branch can still join normal high-velocity recirculation rather than dangling off a long stub, and include the isolation branch in the routine flush/disinfection schedule even on days it isn't used.

6.2 HDF bays — ultrapure water requirements

Online hemodiafiltration (HDF) infuses substitution fluid produced from dialysate directly into the bloodstream, bypassing the dialyzer membrane barrier that protects standard HD — so HDF stations require ultrapure water/dialysate (bacteria <0.1 CFU/mL, endotoxin <0.03 EU/mL), roughly 100–1,000× stricter than standard dialysis water, and a key reason ultrapure water was adopted as standard for high-quality dialysis care (Canaud, 2011).

• Each HDF-capable machine needs its own point-of-use (POU) ultrafilter, typically two in series — one polishing the dialysate, a second "sterilizing-grade" filter immediately upstream of the substitution-fluid infusion line — in addition to the central loop UF.
• POU filters need periodic integrity testing (pressure-hold/diffusion test per manufacturer) and scheduled replacement on the validated interval — do not run them past it even if they "look fine."
• Bay placement: cluster HDF stations on the takeoff closest to the post-RO/UF point on the loop — shortest distance and residence time before the most demanding stations, minimizing bioburden accumulation in transit, and simplifying servicing of the extra POU hardware in one area.

6.3 Dual-pass (double-pass) RO

Used when a single RO pass can't reliably hit ultrapure-grade rejection, or when feed TDS is high (brackish/hard/variable municipal supply).

• Configuration: first-pass permeate becomes the feed to a second RO module instead of raw/pretreated municipal water. Needs an interstage booster pump, because first-pass permeate exits at low pressure and the second membrane still needs its full operating pressure.
• Recovery: first pass typically runs 50–75% recovery (limited by scaling risk from raw feed); second pass runs much higher, often 85–90%+, since its feed is already low-TDS — antiscalant dosing is usually unnecessary on the second pass.
• Reject handling: second-pass reject is usually low enough in TDS to be recirculated back into the first-pass feed, improving overall system recovery — verify this doesn't reconcentrate any problem species for your specific feed water first.
• Array design: first pass commonly uses a tapered ("Christmas tree") membrane array to manage rising reject concentration; second pass is usually a simple single-stage array since its feed is already clean.
• What it buys you vs. UF: double-pass improves ionic/chemical rejection (the conductivity/TDS side). It does not substitute for ultrafiltration — UF (after the loop, plus POU UF at HDF stations) is still required for the microbiological/endotoxin barrier. The two are complementary, not interchangeable.

Water Quality Standards

These are the limits your testing is measured against, per AAMI/ISO 23500 (Suravaram et al., 2024; Humudat et al., 2020). Post this section in the water room.

7.1 Microbiological limits

The "action level" is a trigger, not a pass mark. When a result reaches the action level, investigate and intervene (disinfect, increase monitoring) even though the result hasn't yet exceeded the maximum — acting at the action level is how you avoid ever crossing the limit.

7.2 Maximum allowable chemical contaminants

Maximum concentrations in water used to prepare dialysate, make concentrates from powder, and reprocess dialyzers. Units are mg/L (ppm) unless noted.

Maintenance and Monitoring Schedule

Maintenance is divided between what operating staff do (checks, logging, salt, disinfection) and what biomedical/vendor engineers do (membrane changes, calibration, validation). Adapt frequencies to your manufacturer's manual and DOH requirements (Kasparek & Rodriguez, 2015).

8.1 Routine schedule

8.2 In-house tests you must know how to run

Troubleshooting

Use these matrices to recognize a problem, identify likely causes, and take correct first-line action.

9.1 Water chemistry and RO problems

9.2 Microbiological problems

9.3 System / mechanical

9.4 Step-by-Step Troubleshooting Algorithms

The tables above tell you what to look for. The algorithms below tell you what to do, in order, from the fastest and safest checks to the ones needing biomed or vendor support — with a checklist you can initial as you go. Work each one top to bottom; do not skip to a later step to save time.

9.5 Escalation Contacts

Fill in for your facility and post beside the water log.

Documentation, Logs, and the Water Quality Management Program

DOH AO 2013-0003 requires a documented Water Quality Management Program — defined SOPs, named responsible staff, a calibration and maintenance schedule, and complete, signed records that a surveyor or your medical director can review at any time.

• Daily water log: chlorine/chloramine results, RO conductivity/% rejection, pressures, tank level, disinfection status — dated and signed each shift.
• Disinfection records: date, method, agent and concentration, contact time, and the post-rinse residual test result (negative) for each cycle.
• Laboratory reports: monthly microbiological/endotoxin and six-monthly chemical analyses from a DOH-accredited lab, with evidence that out-of-range results were acted upon.
• Maintenance & calibration logs: filter/cartridge changes, salt refills, carbon rebed, membrane changes, sensor calibration, vendor service reports.
• Corrective action / incident reports: any limit exceedance, pyrogenic reaction, or system failure, with root cause and resolution.

Quick Reference Card

Daily, before the first patient

1. Test TOTAL chlorine after carbon tanks → must be ≤0.1 mg/L. If higher, STOP.
2. Test free chlorine → must be ≤0.5 mg/L.
3. Record RO product conductivity and % rejection.
4. Check feed / RO / loop pressures and storage tank level.
5. Confirm softener has salt and is removing hardness.
6. Confirm any overnight disinfection is fully rinsed (residual negative).
7. Sign the log.

Key limits to remember