Watercalcs
Estimates only — verify before relying on results. Terms of Use
2.0
Guide — Setup
This tool sizes and assesses hollow-fibre UF/MF membrane plants — pressurised or submerged. Start here: pick whether you are designing a new plant or assessing an existing one, choose the membrane type, then enter plant identification. Work left to right through the tabs; every tab has its own guide at the top.
  • New to the tool? Turn on Show worked example below to load a complete, realistic dataset and watch every tab populate.
  • Load a manufacturer template from the ⚙ Settings panel to auto-fill module geometry and integrity test pressures.
  • Tap the blue i for the model basis, assumptions, limitations and references.
Mode
Type
Driver

Plant Identification

Pick a template to auto-fill geometry & test pressures, or just type your own model name. Create and manage templates under ⚙ Settings.
μm

Worked Example

Show worked example
Loads a complete submerged UF dataset so you can see every tab in action. Turn off to clear back to a blank model.

Live summary

New Plant
— enter configuration to see summary —
Clean start: fields are intentionally blank so you can enter your own plant. Method timings (backpulse, chemical backwash and clean-in-place intervals) carry sensible defaults you can change on the Cycles tab. Membrane constants (surface tension, contact angle, pore factor) live under ⚙ Settings.
Guide — Configuration
Define the physical plant: how many trains, the redundancy philosophy, and the module geometry that sets total membrane area. The tiles show area per train, total area, and the flux your configuration produces at design and peak flow so you can check it against the module's flux ceiling.
  • Redundancy N+1 keeps full output with one train out; N+2 with two out.
  • Layout depends on type. Pressurised is train → modules: modules sit side by side in the rack, so you set modules per train and how many rows they form. Submerged is train → cassettes → modules: cassettes are not side by side, so you set cassettes per train and modules per cassette. The repair map draws each accordingly. Membrane area follows from the effective modules per train × area per module.

Train Layout

trains
mod
Pressurised: modules per rack / train.
cass
mod
m²
rows
Pressurised only: how modules sit side by side in the rack (e.g. 2 or 4 rows). Drives the repair map layout.
L
Wetted volume per direct-integrity-test unit (submerged: usually one cassette).

Design Limits

LMH
kPa
LMH/bar

Configuration Summary

Train layout

Guide — Operating
Enter the flow, temperature and feed-water envelope. Minimum, average and peak flows drive the flux scenarios; the temperature range feeds the viscosity normalisation to 20 °C. Feed turbidity and solids are recorded as the fouling context for the plant. Recovery sets the volumetric concentration factor used in the LRV calculation.

Flow & Recovery

m³/d
m³/d
m³/d
%
Design overall recovery. Sets the concentration factor (VCF) for the integrity calculation. The Capacity tab computes the achieved net recovery from the cleaning regime.

Temperature & Feed Water

Condition
°C
°C
°C
NTU
NTU
mg/L
Blank = estimate from turbidity.
mg/L
mg/L
Guide — Cycles & Cleaning
Set the backpulse, chemically enhanced backwash, clean-in-place and membrane integrity test schedule. The tool converts these into per-train downtime and an in-service factor, which reduces net flux and available output on every other tab. Backpulse is triggered by elapsed time or by a TMP setpoint.
  • Effect on production — this is what decides whether an activity is counted as lost output. Choose train offline (the usual case) when the train stops making water for the duration, so the time is subtracted from availability. Choose covered by standby only when a spare train picks up the flow, so the plant keeps producing and no output is lost. It changes the in-service factor, not the work itself.
  • Chemically enhanced backwash — a short chemical dose during a backwash, between full clean-in-place events. Turn it off if the plant backwashes with water only.
Feed condition

Backpulse / Backwash

min
kPa
sec
×
sec
Nm³/h

Membrane Integrity Test

/day
Per train. DWQAR requires at least 1/day.
min
Choose “covered by standby” only if a spare train carries the flow, so plant output is unaffected.

Chemically Enhanced Backwash

Plant uses a chemically enhanced backwash
Turn off if the plant runs water-only backwashes between clean-in-place events. Suppliers use many names for this step (CEB, MC, maintenance clean, chemical wash) — they all mean a short chemical dose during a backwash.
hr
min

Clean-In-Place (CIP)

days
hr
Choose “covered by standby” only if a spare train carries the flow during the clean.

Downtime & In-Service Factor

Guide — Capacity & Redundancy
Two linked questions in one place: how the plant performs at its design point, and whether it holds output when trains drop out for cleaning.
  • Water balance — daily feed, reject, cleaning volumes and net recovery.
  • Flux & permeability — gross flux (while filtering, checked against the max) vs net flux (daily average delivered), and specific flux normalised to 20 °C, at the normal active-train count. Gross flux and redundancy both account for the in-service factor, so they tighten under the dirty-source condition (more backwashing and cleaning). The status column flags capacity limits and permeability loss; a key is shown under the table.
  • Redundancy — gross flux (accounting for cleaning downtime) under simultaneous backwash, chemical backwash, clean-in-place and membrane integrity test outages at worst-case cold, with a pass/fail verdict against the flux ceiling. More frequent cleaning (dirty source) raises the flux and tightens the verdict.
Feed condition

Daily Water Balance

Flux & Permeability — Normal Operation

At the active-train count for the selected redundancy. Gross flux is the flux while filtering (checked against the max design flux); net flux is the lower daily average actually delivered. Because the plant is offline for cleaning part of the time, gross flux rises as cleaning becomes more frequent — so it increases under the dirty-source condition. Specific flux is normalised to 20 °C for season-to-season comparison.

Reading the status:
  • OK — gross flux and permeability are within your design limits.
  • Near limit — gross flux is above 90% of the maximum design flux; little headroom for a turbidity event or a train outage.
  • Flux > max — gross flux (while filtering, after allowing for cleaning downtime) exceeds the maximum design flux. This is a hydraulic capacity problem: add area (modules/cassettes), add a train, reduce the flow this case represents, or reduce cleaning frequency.
  • Low perm. — the specific flux (flux per unit of TMP, normalised to 20 °C) has fallen below your minimum specific-flux floor. The plant may still pass the flux limit, but the membrane now needs more pressure than expected to make its flow. It points to fouling, incomplete cleaning recovery, or membrane ageing rather than a sizing problem — check the TMP trend, CIP effectiveness, and feed-water quality. If it persists at design flux, achievable capacity is being eroded and cleaning or replacement is due.

Redundancy — Outage Scenarios

Guide — Integrity (LRV)
Pressure-decay integrity testing to the USEPA Membrane Filtration Guidance Manual (LT2ESWTR). Enter your test pressures and the measured decay rate; the tool returns the log-removal value (LRV) and, for each target credit, the maximum allowable decay rate — your 4-log alert threshold. It also back-calculates the smallest detectable defect and the test pressure needed for your target resolution.
  • Vsys and Qp must be at the same physical level — both per test unit (e.g. per cassette) or both per train.
  • Membrane constants (surface tension, contact angle, pore shape factor) are under ⚙ Settings.
  • The DWQAR 2026 (T3.PM) compliance panel below checks 3 µm resolution, daily testing, the claimed protozoa credit and the current pass/fail against NZ rules. (The rules call this a “direct integrity test”.)

Integrity Test Parameters

kPa
kPa
kPa
°C
μm
log
kPa/min
min
m³/d
Blank = average flow ÷ active trains. Override to match the level at which Vsys is measured.

Integrity Result

Alert Thresholds

DWQAR 2026 (T3.PM) Compliance

Guide — Fibre Repairs
A running record of pinned or repaired fibres, with a visual map by train and module. Log each repair as you make it; the map shades every module by the number of fibres repaired, so recurring damage stands out at a glance. Pinned fibres are a small permanent loss of area and a common driver of gradual integrity decline — tracking them supports your integrity programme and cleaning/replacement decisions. Set your supplier’s repair limit per module under ⚙ Settings; modules are flagged as they approach it and again once it is reached.

Log a Repair

Repair Map

Repair Log

Guide — Report & Save
The single place to get data out of the tool. Choose the sections you want, then export a formatted PDF report or a CSV of inputs and results. Save writes a JSON file of everything to your downloads folder; Load restores it later. Nothing is uploaded anywhere — all files stay on your device.

Select Sections to Export

Export

Save & Load

Save the full model — all inputs, settings and custom templates — as a JSON file you can archive or share. Load it back to pick up exactly where you left off.