Ro Rejection Rate Calculator

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RO Rejection Rate Calculator

Salt Rejection Rate:
0%
function calculateRORejection() { var feed = parseFloat(document.getElementById('feedTDS').value); var permeate = parseFloat(document.getElementById('permeateTDS').value); var resultBox = document.getElementById('roResultBox'); var resultValue = document.getElementById('rejectionPercent'); var statusText = document.getElementById('rejectionStatus'); if (isNaN(feed) || isNaN(permeate) || feed feed) { alert('Permeate TDS cannot be higher than Feed TDS.'); return; } var rejectionRate = ((feed – permeate) / feed) * 100; resultBox.style.display = 'block'; resultValue.innerHTML = rejectionRate.toFixed(2) + '%'; if (rejectionRate >= 95) { statusText.innerHTML = "Excellent Performance: Your RO membrane is highly efficient."; statusText.style.color = "#28a745"; } else if (rejectionRate >= 90) { statusText.innerHTML = "Good Performance: The system is operating within normal ranges."; statusText.style.color = "#fd7e14"; } else { statusText.innerHTML = "Low Performance: Consider cleaning or replacing the RO membrane."; statusText.style.color = "#dc3545"; } }

Understanding RO Rejection Rate

The Reverse Osmosis (RO) Rejection Rate is a critical performance metric used to determine how effectively an RO membrane is removing dissolved solids from water. It measures the percentage of Total Dissolved Solids (TDS) that the membrane successfully blocks from passing into the clean water stream (the permeate).

The RO Rejection Formula

The calculation is based on the difference between the source water (feed) and the filtered water (permeate). The standard formula is:

Rejection Rate (%) = [(Feed Water TDS – Permeate TDS) / Feed Water TDS] × 100

Practical Example

Suppose you test your incoming tap water (Feed Water) and find it has a TDS of 400 ppm. After passing through your RO system, you test the filtered water (Permeate) and it shows 20 ppm. Using the calculator:

  • Feed TDS: 400 ppm
  • Permeate TDS: 20 ppm
  • Calculation: [(400 – 20) / 400] × 100 = 95%

In this scenario, your system has a 95% rejection rate, which is considered very good for most residential systems.

What is a Good Rejection Rate?

Most modern Thin Film Composite (TFC) membranes are designed to reject between 95% and 99% of dissolved solids. Here is a general guide to interpreting your results:

Rejection Rate Status
96% – 99% Excellent – Optimal Membrane Performance
90% – 95% Acceptable – Standard operational range
Below 90% Poor – Membrane may need replacement or cleaning

Factors Affecting Performance

Several variables can influence your system's rejection rate, even if the membrane is relatively new:

  • Water Pressure: RO membranes require specific pressure (usually 40-60 psi for residential) to function correctly. Low pressure results in lower rejection rates.
  • Water Temperature: Extremely cold water can reduce the flow and efficiency of the membrane.
  • TDS Concentration: Very high levels of incoming TDS can put more strain on the membrane, slightly lowering the rejection efficiency.
  • Membrane Age: Over time, membranes can scale or foul, leading to a decrease in the rejection rate.

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