- Enter the number of standard HD stations and online HDF stations expected to run at the same time (peak simultaneous use) — not your total station count.
- Adjust the per-station flow assumptions only if your machines/prescriptions differ from the defaults (40 L/hr standard HD, 55 L/hr HDF).
- Set a design margin (default 25%) and, if your feed water runs cold, a feed temperature for RO derating (RO output drops ~2.5%/°C below 25°C).
- Optionally enter your RO's rated capacity (at 25°C) to get a headroom verdict. Leave it blank to see only the required capacity.
All computation runs in your browser; no values are stored or transmitted.
When to Use
Use this whenever you are planning to add hemodialysis stations (new build, unit expansion, adding a shift, or converting stations to online HDF) and need to know whether the existing — or a proposed — reverse osmosis (RO) system can supply them, and whether pretreatment (softener, carbon tanks) needs to scale alongside it.
Appropriate use
Facility planning, capacity audits before adding machines or shifts, and sanity-checking a vendor's proposed RO size against your unit's actual peak demand.
When NOT to rely on it
This estimates water production capacity only. It does not size the distribution loop, recirculation pump, storage tank, or pretreatment train (softener grain capacity, carbon tank Empty Bed Contact Time) — all of which must scale with the RO or become the actual bottleneck. It also does not replace a validated engineering assessment by your biomedical engineer or RO vendor before a facility expansion.
Pearls & Pitfalls
Peak simultaneous stations, not total stations
A 20-station unit running two staggered shifts of 10 has a peak demand of 10 stations, not 20 — size the RO to what actually runs at the same time, with margin, not to the building's total chair count.
Temperature matters more than it looks
An RO rated at 25°C can lose 20%+ of its output on a run of consistently cooler feed water. If your facility's feed water is reliably cooler than 25°C (early-morning well water, cool season), the derated figure — not the nameplate figure — is the number to plan against.
Pitfalls
(1) A large storage tank can mask an undersized RO for a while — compare demand against the RO's rated production rate, not tank volume. (2) Adding RO capacity without scaling the carbon tanks reduces Empty Bed Contact Time and risks chloramine breakthrough — treat this calculator's output as the RO-sizing half of the problem, not the whole system. (3) "Sufficient" headroom here still requires the distribution loop and recirculation pump to maintain adequate velocity with the added branch takeoffs.
Water Treatment Capacity Calculator
Enter peak simultaneous stations by modality, adjust assumptions if needed, and (optionally) your RO's rated capacity to get a headroom verdict.
⚕ Estimates water-production capacity only — pretreatment (softener, carbon EBCT), storage, and distribution-loop velocity must be verified separately. See the Water Treatment Systems reference §5–6. For licensed clinicians and biomedical engineers; not a substitute for a validated facility engineering assessment.
Next Steps
Use the required-capacity figure to decide whether — and how — to scale up, not just whether to add machines.
- If headroom is marginal or insufficient, the preferred fix is a parallel RO skid sized to at least the shortfall — this gives N+1 redundancy rather than replacing the existing unit.
- Scale pretreatment (softener grain capacity, carbon tank Empty Bed Contact Time) alongside any RO increase — pushing more flow through the same carbon tanks risks chloramine breakthrough.
- Re-check the distribution loop pipe diameter and recirculation pump against the new peak flow before adding stations.
- Re-validate (conductivity/rejection, chlorine, microbiological/endotoxin) and update the facility's Water Quality Management Program before the added stations treat patients.
- See the full Hemodialysis Water Treatment Systems guide for source-water-specific design, facility layout, and troubleshooting.
Evidence & References
Formula
| Quantity | Formula |
|---|---|
| Peak demand (L/hr) | (standard HD stations × standard flow) + (HDF stations × HDF flow) |
| Margin-adjusted demand (L/hr) | peak demand × (1 + margin/100) |
| Required RO capacity, temperature-derated (L/hr) | margin-adjusted demand ÷ (1 − 0.025 × max(0, 25 − feed temp °C)) |
| Headroom | (rated RO capacity − required capacity) ÷ rated RO capacity |
Per-station flow defaults (40 L/hr standard HD, 55 L/hr online HDF) and the 2.5%/°C RO temperature-derating approximation reflect typical ranges described in the water-management literature; always verify against your specific RO manufacturer's temperature-correction table and your unit's actual dialysate flow prescriptions.
References
- Kasparek T, Rodriguez OE. What Medical Directors Need to Know about Dialysis Facility Water Management. Clin J Am Soc Nephrol. 2015;10(6):1061-1071.
- Suravaram S, Gopikonda SS, Siddiqui IA, et al. Enhancing infection control in dialysis at a resource limited public healthcare institute: microbiological quality assessment of dialysis water and dialysate (ANSI/AAMI RD47:2020, ISO 23500-4:2019). Indian J Med Microbiol. 2024;52:100734.
