RO Recovery and Concentrate Calculator
Recovery sets both your water yield and your scaling risk. Enter feed and permeate flows — or a target recovery — plus feed TDS to get recovery, concentrate flow, and concentrate TDS.
RO Mass Balance
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How the calculation works
Formulas
Recovery (%) = permeate flow ÷ feed flow × 100
Concentrate flow (gpm) = feed flow − permeate flow
Permeate TDS (mg/L) ≈ feed TDS × (1 − rejection)
Concentrate TDS (mg/L) = (feed TDS − recovery fraction × permeate TDS) ÷ (1 − recovery fraction)
Concentration factor = 1 ÷ (1 − recovery fraction)
Recovery (%) = permeate flow ÷ feed flow × 100
Concentrate flow (gpm) = feed flow − permeate flow
Permeate TDS (mg/L) ≈ feed TDS × (1 − rejection)
Concentrate TDS (mg/L) = (feed TDS − recovery fraction × permeate TDS) ÷ (1 − recovery fraction)
Concentration factor = 1 ÷ (1 − recovery fraction)
Notes & limitations
The concentrate TDS comes from a steady-state salt mass balance: feed salt = permeate salt + concentrate salt. It is an estimate — actual concentrate chemistry depends on individual ion rejection, and precipitation of sparingly soluble salts (calcium carbonate, calcium sulfate, silica) can remove mass from solution.
- Higher recovery means a more concentrated brine and a higher scaling risk. Check scaling indices (Langelier / Stiff-Davis) on the concentrate before pushing recovery up.
- Typical brackish-water RO recovery is 75–85%; seawater RO is often 40–50%. Design values come from membrane projection software, not from this screening tool.
- Salt rejection varies by membrane age, temperature, and pressure. Use the manufacturer’s rated rejection at your operating conditions, and verify with permeate conductivity.
- This tool assumes steady state with no salt precipitation and no blend streams. Confirm against plant mass-balance records.