Water Engineering Tools
High-precision calculators, membrane mass balances, and chemical projection models built for water process engineers and desalination specialists.
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Engineering Workflows
RO System Analysis
Follow a membrane system from feedwater to design review, one calculation at a time.
- Feedwater Define feed source and quality
- 1 Recovery Permeate vs concentrate flow
- 2 Mass Balance Salt and flow balance across membranes
- 3 Permeate / Concentrate Quality and concentrate load
- 4 Osmotic Pressure Net driving pressure check
- 5 Scaling Risk LSI / S&DSI tendency
- 6 Design Review Explore staged design scenarios
Treatment Train: UF → NF → RO
Connect membrane stages into one train: a value moves only through a validated stream port, conversions are named, and the stages downstream recalculate automatically.
- 1 Build the Train Add stages, connect stream ports, run the engines
- 2 UF Membrane Area Size the ultrafiltration stage from flux and flow
- 3 NF Water Balance Split the NF feed into permeate and concentrate
- 4 RO Recovery Set the reverse osmosis stage recovery
- 5 IX Bed Sizing Size a polishing bed and its EBCT
Featured Tools
RO Recovery Calculator
RO recovery and permeate flow with full water and salt balance closure, concentrate concentration and salt loads.
Recovery (%) = (Permeate Flow / Feed Flow) × 100 RO Salt Rejection Calculator
Calculate membrane salt rejection percentage from feed and permeate TDS concentrations.
Rejection (%) = (1 - (Cp / Cf)) × 100 RO Permeate TDS Calculator
Project expected permeate total dissolved solids based on feed water salinity and rejection specs.
Cp = Cf × (1 - R / 100) Water Engineering Disciplines
Reverse Osmosis (RO)
Membrane recovery, mass balance, salt rejection, and permeate quality.
Explore tools →Desalination Systems
Membrane desalination energy, recovery, mass balance and sizing for RO plant design.
Explore tools →Water Treatment
Coagulation, filtration, softening, and chemical dosing.
Explore tools →Water Quality & Chemistry
Langelier Saturation Index (LSI), TDS conversion, and conductivity.
Explore tools →Hydraulics & Pumping
Pipe friction loss, pump sizing, Darcy-Weisbach, and Hazen-Williams.
Explore tools →Water Resources & Hydrology
Watershed yield, storm runoff, and water storage balances.
Explore tools →Plumbing & Water Supply
Drainage fixture units, supply demand, septic tanks, rainwater harvesting and sump pumps.
Explore tools →Environmental Water Management
Greywater reuse, irrigation demand, infiltration trenches, soakaways and bioswales.
Explore tools →All Water Engineering Tools
58 ToolsRO Recovery Calculator
RO recovery and permeate flow with full water and salt balance closure, concentrate concentration and salt loads.
Recovery (%) = (Permeate Flow / Feed Flow) × 100 RO Salt Rejection Calculator
Calculate membrane salt rejection percentage from feed and permeate TDS concentrations.
Rejection (%) = (1 - (Cp / Cf)) × 100 RO Salt Passage Calculator
Determine salt passage percentage through RO membranes and verify complementary rejection balance.
Passage (%) = (Cp / Cf) × 100 RO Permeate TDS Calculator
Project expected permeate total dissolved solids based on feed water salinity and rejection specs.
Cp = Cf × (1 - R / 100) RO Concentrate Flow Calculator
Brine/reject flow with water and salt balance closure, concentrate TDS, concentration factor and salt loads.
Qc = Qf - Qp = Qf × (1 - Y / 100) RO Osmotic Pressure Calculator
Estimate RO feed osmotic pressure using a simplified van’t Hoff model from TDS, temperature, and solute properties.
π = i × C × R × T RO Design Studio
Build a preliminary RO system design with feed inputs, staging, custom membrane data, sequential element estimates, balances, and warnings.
Q = A × S × (ΔP − Δπ) RO Mass Balance Calculator
Simplified TDS-based dissolved-solids balance for RO feed, permeate, and concentrate flow and quality checks.
Qf · Cf = Qp · Cp + Qc · Cc RO Scaling Risk & Pretreatment Analysis
Screen CaCO3 scaling risk in RO feed and concentrate using the Langelier Saturation Index (ASTM D3739) and the Stiff & Davis Stability Index (S&DSI) for high-TDS and seawater feeds.
LSI = pH − pHS · S&DSI = pH − pCa − pAlk − K RO Energy & Specific Power Calculator
Determine specific energy consumption (kWh/m³) based on operating pressure and pump efficiency, with optional energy recovery device savings.
SEC = Q_f × P / (36 × η_p × Q_p) · P_h = Q_f × P / 36 · P_erd = Q_b × P × η_erd RO Operating Cost (OPEX) & SEC Calculator
Estimate RO operating expenditure: pumping energy (specific energy consumption), chemical cleaning, antiscalant, and membrane replacement.
SEC = P_feed × Q_f/(η_pump·Q_p) · OPEX = Σ (energy + chemical + membrane + maintenance) RO Performance & Troubleshooting Analyzer
Compare a current measured RO run against its commissioning baseline: permeate flow normalized to 25 °C and baseline net driving pressure (ASTM D4516-style), salt passage, pressure drop, flux and specific flux — with directional, verify-in-the-field diagnostics.
Qn = Qm × (TCF_ref/TCF_use) × (NDP_ref/NDP_use) with TCF ≈ 1.03^(T−25) and NDP = P_feed,avg − P_perm − (π_feed − π_perm) Plant Mass Balance
Assemble the whole plant as an ordered chain of unit operations: raw intake to product and waste, stage-to-stage product flow, external make-up, derived concentrate TDS by salt conservation, and plant-wide water and salt balance checks.
product = feed × recovery/100 · waste = feed − product · Cw = (Qf·Cf − Qp·Cp)/Qw · intake + make-up = plant product + plant waste Water Analysis & Treatment Selection
Enter a feedwater analysis once: derive hardness, cation–anion charge balance, TDS by summation, ionic strength and saturation indices (LSI/RSI), then compare water-quality drivers against the treatment surfaces already built on the platform — a qualitative start, not a diagnosis.
hardness = 2.497·Ca + 4.118·Mg · balance% = 200·(Σmeq+ − Σmeq−)/(Σmeq+ + Σmeq−) · LSI/RSI via existing saturation engine Small & Modular Desalination Sizing
Size a small or modular desalination plant from a demand basis forward: community population to product flow, then feed and concentrate by the plant mass balance, then membrane area, vessels and staging. Composes engines that already exist; chooses no recovery, staging ratio, flux or package envelope.
No new formula: composes calculateWaterDemand → analyzePlantMassBalance → buildRoArray → buildModularPackageScope. Feed = product ÷ recovery; area = permeate ÷ design flux; vessels = area ÷ element area × elements per vessel. Filter Sizing Calculator
Size a conventional rapid-gravity multimedia filter from design flow, filtration rate, bed depth and media effective size: required filter area, design area after the engineer's safety factor, and media volume. The unit count needs a stated catalogue unit area, and no clean-water head loss is invented.
A = Q/v · design area = A × safety factor · units = ceil(design area / unit area) only when a catalogue unit area is supplied · media volume = design area × depth · no head loss is computed Cartridge Filter Sizing Calculator
Size cartridge and bag filter elements and housings from design flow, feed solids and the manufacturer's element flow rating: hourly solids load, element count and housing count. No element size is assumed and no differential pressure is invented.
solids load (g/h) = Q × feed solids · elements = ceil(Q / element flow rating) × safety factor · housings = ceil(elements / elements per housing) · no differential pressure is computed Disinfection CT Value Calculator
Compute the achieved CT value from residual disinfectant concentration and contact time, compare it against a required CT you state from your disinfection reference, and get the contact time the design needs to reach it.
CT = residual concentration × contact time · margin = (achieved − required) / required · contact time needed = required CT / residual · no required CT and no UV dose are built in Ultrafiltration (UF) Membrane Engineering
Size UF membrane area from permeate flow and design flux, compute transmembrane pressure from the feed/filtrate/concentrate pressures, and read normalised flux against the reference condition to expose fouling.
A = Qp/flux · TMP = Pf − (Pfilt + Pc)/2 · normalised flux against reference temperature Nanofiltration (NF) Membrane Engineering
Close the NF water and solute balance from a stated recovery and rejection to get permeate and concentrate flow and TDS, then size membrane area from the permeate flux.
Qp = Qf·Y · Qc = Qf − Qp · solute balance Qf·Cf = Qp·Cp + Qc·Cc · A = Qp/flux Ion Exchange (IX / IER) Bed Sizing
Size an ion exchange bed from service flow, resin volume and empty-bed contact time, and compute stoichiometric regenerant demand from the ionic loading.
V = Q·EBCT · service flow = Q/A · regenerant mass from stoichiometric ionic loading RO Concentration Factor & Salt Load Calculator
Compute RO water concentration factor (CF = 1/(1−Y)) and the salt load carried to concentrate for scaling and disposal analysis.
CF = 1 / (1 − Y) · Salt Load = Q_f × C_f × Y_loading RO Feed Pressure & Specific Energy Calculator
Estimate required RO feed pressure (permeate osmotic gap + net driving pressure) and specific energy consumption with optional energy recovery.
P_feed ≈ Δπ + (J × 100/B·SCP factor) + ΔP_friction RO Antiscalant & Chemical Dosing Calculator
Calculate antiscalant (or chemical) dosing rate and 100% active-equivalent flow from dose concentration and product strength.
Dose Flow = Q_feed × Dose_ppm / (C_prod × 100) (SG-adjusted) RO Membrane & Vessel Element Count Calculator
Calculate number of RO membrane elements and pressure vessels from permeate flow, design flux, and element area.
Elements = Q_p / (Flux × A_element) · Vessels = ⌈Elements / Elements per Vessel⌉ Desalination Plant Designer
Compose a whole desalination plant as an ordered chain of unit operations from raw intake to product and waste: design basis, stage recoveries and make-up, whole-plant water and salt balance checks, and concentrate TDS derived by salt conservation — every value labelled input, derived or missing.
plant recovery = final product / raw intake · stage product = feed × recovery/100 · concentrate TDS: Qw·Cw = Qf·Cf − Qp·Cp · membrane product TDS: Cp = Cf × (1 − R/100) Pump Power Calculator
Calculate hydraulic power, shaft power, and motor electrical power from head and flow rate.
HPump = ρ × g × Q × H / η Engineering Unit & Water Quality Converter
Convert flow rates and TDS concentration units (mg/L ↔ ppm) using the Site canonical unit engines (m³/day internal).
Canonical flow unit = m³/day · 1 mg/L ≈ 1 ppm (dilute aqueous) Pipe Flow & Friction Loss Calculator
Determine pipe velocity, friction head loss, and pressure drop via Darcy-Weisbach or Hazen-Williams.
v = Q / A · hf = 10.67 × L × Q^1.852 / (C^1.852 × D^4.871) Open Channel Flow (Manning′) Calculator
Compute open-channel velocity and discharge with Manning’s equation for trapezoidal, rectangular, and circular channels.
v = (1/n) × R^(2/3) × S^(1/2) · Q = v × A Pipe Flow Velocity & Sizing Calculator
Size a pipe to carry a target flow within a recommended velocity range, or check velocity for a given diameter.
D = √(4Q / (π·v)) · v = Q / A Reynolds Number & Flow Regime Calculator
Calculate Reynolds number for pipe flow and classify the flow regime (laminar / transitional / turbulent).
Re = ρ·v·D / μ Pipe Pressure Drop (Darcy–Weisbach) Calculator
Compute pipe head loss and pressure drop with the Darcy–Weisbach equation, solving the Colebrook friction factor.
hf = f × (L/D) × (v²/2g) · f via Colebrook-White Pump Head / Total Dynamic Head Calculator
Compose total dynamic head from static lift, friction losses, minor losses, and residual pressure.
TDH = H_stat + h_friction + h_minor + h_residual Pressure & Head Unit Converter
Convert pressure and head units: bar, kPa, MPa, psi, m H₂O, ft H₂O, and atmospheres.
1 bar = 100 kPa = 14.5038 psi = 10.197 m H₂O Volumetric → Mass Flow Converter
Convert volumetric flow to mass flow (and reverse) using fluid density, with common water/TDS basis.
ṁ = ρ × Q · Q = ṁ / ρ Water Quality Saturation Indices (LSI & RSI)
Evaluate calcium carbonate stability of a water with the Langelier Saturation Index (LSI) and Ryznar Stability Index (RSI) from pH, temperature, TDS, calcium, and alkalinity.
pH_s = 9.3 + A + B − C − D · LSI = pH − pH_s · RSI = 2·pH_s − pH Water Tank Storage Calculator
Size cylindrical and rectangular water storage tanks from dimensions or daily demand and residence time.
V = π/4 × D² × H · V = L × W × H Water Demand & Flow Requirement Calculator
Estimate community or facility water demand (domestic, commercial, fire) and the design flow requirement for supply and storage sizing.
Q_design = P · q · peakFactor · Q_avg = V_daily / 86400 Tank Fill Time & Filling Rate Calculator
Calculate the time to fill a storage tank from a known filling rate, or the filling rate required to meet a target time.
t = V / Q · Q = V / t Sodium Metabisulphite Dosing Calculator
Dose sodium metabisulphite from the chlorine residual it must neutralise or the sulphite level it must hold, using the stoichiometric ratio and your product strength. No chlorine residual and no product strength are assumed.
SMBS = Cl₂ demand × 190.12/70.90 (1 mol each), or sulphite target ÷ 2 (1 mol SMBS yields 2 mol SO₃²⁻) · product mass = active ÷ the certificate assay when one is given, else ÷ nominal strength — the assay replaces the strength, never both · no finished pH is predicted Coagulant Dosing Calculator
Turn a jar-test coagulant dose into active metal and product mass per day, from the dose basis you measured and the product active content. The dose is your jar test and the pH outcome is not predicted.
active metal (kg/h) = Q × dose ÷ 1000 · product (kg/day) = active ÷ active content · safety factor applies to both so they cannot disagree · no pH is predicted Clarifier Sizing Calculator
Size a circular or rectangular clarifier from the surface overflow rate, then check it against the solids loading when you state both. Reports which criterion governs and never predicts a solids removal.
area = Q ÷ SOR · load-based area = (Q × 24 × SS × removal%) ÷ (1000 × capacity) · governing criterion is reported · detention time is a consequence, not a criterion Activated Sludge Sizing Calculator
Size an aeration basin from the applied COD load, the F/M loading and the MLVSS, then audit your stated SRT, HRT and volume against each other. Reports oxygen demand as demand only, never as air flow.
load = Q × S₀ ÷ 1000 · V = load ÷ (F/M × X) on the APPLIED load · Px = Yobs × load removed · θc = VX ÷ Px · wasting = inventory ÷ θc · O₂ = 8/7 × COD removed, +4.57 per kg NH₄-N removed · air flow is not calculated GAC Contactor Sizing Calculator
Size a granular activated carbon bed from the empty bed contact time you selected, giving the bed volume, media mass and backwash shell volume. Breakthrough and contaminant removal are not predicted.
bed volume = Q × EBCT ÷ 60 · media mass = bed volume × bulk density · backwash shell = bed volume × (1 + expansion) · breakthrough and removal are NOT predicted UV Disinfection Sizing Calculator
Size a UV reactor bank from the required dose and design flow, then count parallel reactors against the out-of-service allowance. The ideal power is stated separately from the validated reactor power.
required power = Q × dose (1 mJ/cm² over 1 m³/h is 1 W) · reactors = ceil(required ÷ (module power × duty factor)) · annual energy is nameplate × availability CIP Tank Sizing Calculator
Size CIP cleaning and storage tanks from your cleaning protocol volume per element and the heel the tank retains, with separate alkaline, acid and neutral volumes and optional annual chemical consumption.
cleaning volume = elements × protocol volume per element · tank volume = cleaning volume ÷ (1 − heel) because the heel is retained · annual chemical = mass × cleanings per year Brine Volume and Mass Calculator
Annualise the brine volume and salt mass from the concentrate stream, with optional disposal cost and the dilution arithmetic against a stated permit limit. No compliance verdict is issued.
annual volume = brine flow × operating hours · salt mass = TDS × volume ÷ 1e6 to tonnes · dilution = Q × (C − limit) ÷ limit · no compliance verdict is issued Drainage Fixture Unit Calculator
Total drainage fixture units and the minimum building drain from fixture counts under the IPC or UPC tables.
Total DFU = sum(n x DFU) ; building drain from the code sizing table Water Supply Fixture Unit Calculator
Total water supply fixture units converted to an estimated peak demand in gallons per minute and a typical service size.
Total WSFU = sum(n x WSFU) ; peak demand interpolated from the Hunter flush-tank curve Septic Tank Sizing Calculator
Septic tank volume and standard size from residents, daily flow, retention time and the sediment storage allowance.
V = n x q x (t/24) x sediment factor Rainwater Harvesting Calculator
Annual and monthly rainwater yield from a roof, with a cistern size derived from a daily demand and autonomy period.
V_year = A x (P/1000) x C x efficiency Sump Pump Sizing Calculator
Inflow to a sump from the drainage area and design rainfall, with the safety-factored pump capacity and hydraulic power.
Q = A x (i/1000) x C / 3600 ; P = rho g Q H / eta Greywater Reuse Calculator
Reusable greywater available per day and the storage volume needed, from residents, laundry flow and the captured fraction.
Q_reuse = (n x q_person + q_laundry) x capture fraction Irrigation Demand Calculator
Daily and weekly irrigation water requirement from reference evapotranspiration, crop factor and system efficiency.
V = A x (ET0 x Kc) / (1000 x efficiency) Infiltration Trench Calculator
Length and drain time of an infiltration trench from the stored runoff volume, void ratio and soil infiltration rate.
V = A x P x C ; V_trench = V / void ratio ; t = V / (k x base area) Soakaway Calculator
Soakaway storage and base area from a percolation test result, the drainage area and the design storm.
k = 1000 / percolation time ; V = A x P x C ; A_base = V / depth Bioswale Calculator
Trapezoidal bioswale geometry, storage volume, media void storage and drawdown time for a given infiltration rate.
A = (b + z d) d ; V = A L ; t = V / (k P L) Knowledge & Resources
Pretreatment Design
Select and size filtration, conditioning and membrane-protection barriers.
Explore →Worked Engineering Examples
Evidence-backed treatment cases you can open and change in Plant Designer.
Explore →Technical Guides
Aquifer storage & recovery, filtration, desalination concepts.
Explore →Engineering Concepts
RO recovery, osmotic pressure, membrane selection.
Explore →Equipment References
Pumps, membranes, pressure vessels, energy recovery.
Explore →Manufacturers
Membrane and RO component manufacturers.
Explore →Desalination Projects
Source-backed SWRO plant case studies.
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