What this permeate blending calculator does

Permeate blending calculator mixes raw water (conductivity/TDS = C_r) and RO permeate (C_p) to reach a target conductivity/TDS (C_t). It returns the required permeate fraction and split flows (Q_p, Q_r) for a specified total blend flow. Results are shareable by URL and can be exported to CSV, so engineers and operators review the same assumptions and numbers.

When to use it

• Finished water must stay within a conductivity/TDS window (e.g., drinking, boiler feed, process rinsing).
• You want to blend back a small portion of raw water to reduce cost or adjust alkalinity/feel.
• During pilot/commissioning, you need fast estimates of ratios and flows at different set points.

Inputs explained

• Value unit: μS/cm (conductivity) or TDS (mg/L). Keep units consistent across inputs.
• Raw water (C_r): feed conductivity/TDS.
• Permeate (C_p): RO permeate conductivity/TDS.
• Target (C_t): desired conductivity/TDS of the blended stream.
• Total blend flow: target mixed flow; the tool outputs Q_p and Q_r.

Mass balance & formula

Assuming linear mixing at similar temperature and CO₂ state:

C_t = f_p·C_p + (1 − f_p)·C_r ⇒ f_p = (C_t − C_r) / (C_p − C_r).
Then Q_p = f_p·Q_total and Q_r = (1 − f_p)·Q_total.

Worked example

C_r=1500 μS/cm, C_p=60 μS/cm, C_t=200 μS/cm, Q_total=1000 LPH.
f_p = (200−1500)/(60−1500) = 1300/1440 ≈ 90.3%.
Q_p ≈ 903 LPH, Q_r ≈ 97 LPH.

Units & quick conversions

Good practice & caveats

• Sample and blend at similar temperature; large differences affect readings.
• Conductivity/TDS depends on ion makeup; if CO₂ equilibrium or dosing reactions change, verify on site and keep a safety margin.
• This permeate blending calculator is an engineering estimate; finalize set points with online instruments and trend data.

Related reading

For scaling/corrosion tendency, see an overview of the Langelier Saturation Index (LSI). Use LSI alongside antiscalant design and temperature-corrected measurements.

From calculator to configured package

Need a configured reference? See the 1000 LPH RO Water Treatment Solution (architecture, KPIs and O&M guidance). You can also model operating cost with our RO OPEX Calculator.

What this permeate blending calculator does

Permeate blending calculator mixes raw water (conductivity/TDS = C_r) and RO permeate (C_p) to reach a target conductivity/TDS (C_t). It returns the required permeate fraction and split flows (Q_p, Q_r) for a specified total blend flow. Results are shareable by URL and can be exported to CSV.

When to use it

• Finished water must stay within a conductivity/TDS window (e.g., drinking, boiler feed, process rinsing).
• You want to blend back a small portion of raw water to reduce cost or adjust alkalinity/feel.
• During pilot/commissioning, you need fast estimates of ratios and flows at different set points.

Inputs explained

• Value unit: μS/cm (conductivity) or TDS (mg/L). Keep units consistent across inputs.
• Raw water (C_r): feed conductivity/TDS.
• Permeate (C_p): RO permeate conductivity/TDS.
• Target (C_t): desired conductivity/TDS of the blended stream.
• Total blend flow: target mixed flow; the tool outputs Q_p and Q_r.

Mass balance & formula

Assuming linear mixing at similar temperature and CO₂ state:
C_t = f_p·C_p + (1 − f_p)·C_r ⇒ f_p = (C_t − C_r) / (C_p − C_r).
Then Q_p = f_p·Q_total and Q_r = (1 − f_p)·Q_total.

Worked example

C_r=1500 μS/cm, C_p=60 μS/cm, C_t=200 μS/cm, Q_total=1000 LPH.
f_p = (200−1500)/(60−1500) = 1300/1440 ≈ 90.3%.
Q_p ≈ 903 LPH, Q_r ≈ 97 LPH.

Good practice & caveats

• Sample and blend at similar temperature; large differences affect readings.
• Conductivity/TDS depends on ion makeup; if CO₂ equilibrium or dosing reactions change, verify on site and keep a safety margin.
• This tool is an engineering estimate; finalize setpoints with online instruments and trend data.

Need a configured reference? See the 1000 LPH RO Water Treatment Solution (architecture, KPIs and O&M guidance).

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