Ro Rejection Rate Calculation

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RO Rejection Rate Calculator .ro-calc-container { max-width: 800px; margin: 0 auto; font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif; color: #333; background: #fff; padding: 20px; border-radius: 8px; box-shadow: 0 4px 15px rgba(0,0,0,0.05); } .ro-calc-header { text-align: center; background: #0288d1; color: white; padding: 20px; border-radius: 8px 8px 0 0; margin: -20px -20px 20px -20px; } .ro-calc-header h2 { margin: 0; font-size: 24px; } .ro-input-group { margin-bottom: 20px; } .ro-input-group label { display: block; margin-bottom: 8px; font-weight: 600; color: #0277bd; } .ro-input-group input { width: 100%; padding: 12px; border: 1px solid #ddd; border-radius: 4px; font-size: 16px; box-sizing: border-box; } .ro-input-group input:focus { border-color: #0288d1; outline: none; box-shadow: 0 0 5px rgba(2, 136, 209, 0.2); } .ro-input-help { font-size: 12px; color: #666; margin-top: 4px; } .ro-btn-container { text-align: center; margin-top: 25px; } .ro-btn { background-color: #0288d1; color: white; border: none; padding: 12px 30px; font-size: 16px; border-radius: 4px; cursor: pointer; transition: background-color 0.3s; font-weight: bold; } .ro-btn:hover { background-color: #01579b; } .ro-result-box { margin-top: 30px; padding: 20px; background-color: #e1f5fe; border-radius: 6px; border-left: 5px solid #0288d1; display: none; } .ro-result-value { font-size: 32px; font-weight: bold; color: #01579b; margin-bottom: 10px; } .ro-result-status { font-weight: bold; font-size: 18px; margin-top: 10px; } .status-excellent { color: #2e7d32; } .status-good { color: #558b2f; } .status-fair { color: #f9a825; } .status-poor { color: #c62828; } .ro-content-section { margin-top: 50px; line-height: 1.6; border-top: 1px solid #eee; padding-top: 20px; } .ro-content-section h3 { color: #0277bd; border-bottom: 2px solid #e1f5fe; padding-bottom: 10px; margin-top: 30px; } .ro-content-section p { margin-bottom: 15px; } .ro-content-section ul { background: #f9f9f9; padding: 20px 40px; border-radius: 6px; } .ro-content-section li { margin-bottom: 10px; } @media (max-width: 600px) { .ro-calc-container { padding: 15px; } }

RO Rejection Rate Calculator

The Total Dissolved Solids of the water entering the RO system.
The Total Dissolved Solids of the purified water coming out.
Calculated Rejection Rate:
0.00%

Understanding RO Rejection Rate

The Reverse Osmosis (RO) Rejection Rate is a critical performance metric for any water filtration system. It represents the percentage of dissolved solids (contaminants) that the RO membrane successfully removes from the feed water. Monitoring this percentage is the standard method for determining the health and efficiency of your RO membrane.

How to Calculate Rejection Rate

The formula for calculating the rejection rate is based on the Total Dissolved Solids (TDS) levels of the water entering the system versus the water leaving the system. TDS is typically measured in parts per million (ppm) or milligrams per liter (mg/L).

Formula:

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

Example: If your tap water (Feed) has a TDS of 400 ppm and your filtered water (Permeate) has a TDS of 20 ppm:

  • Calculation: (400 – 20) / 400 = 0.95
  • Result: 0.95 × 100 = 95% Rejection Rate

Interpreting Your Results

Different RO membranes are rated for different rejection efficiencies. However, standard residential and commercial TFC (Thin Film Composite) membranes generally follow these guidelines:

  • 97% – 99%+: Excellent. The membrane is operating at peak efficiency.
  • 95% – 97%: Good. Standard performance for many residential systems.
  • 90% – 95%: Fair. The membrane may be aging, or water pressure/temperature may be low. Monitor closely.
  • Below 90%: Poor. It is likely time to replace the RO membrane, as it is passing too many contaminants.

Factors Affecting Rejection Rate

If your calculation shows a lower rate than expected, consider these factors before replacing the membrane:

  • Water Pressure: RO membranes require high pressure to function. Low residential pressure (< 40 PSI) drops rejection rates.
  • Temperature: Cold water reduces the diffusion rate, which can lower system output and alter rejection slightly.
  • TDS Creep: If you measure TDS immediately after the system turns on, the reading may be high. Let the water run for 60 seconds before testing.
  • Membrane Age: Over time, membranes foul and degrade due to chlorine exposure or sediment buildup.
function calculateRejectionRate() { // 1. Get input values var feedTDS = document.getElementById('feedTDS').value; var permeateTDS = document.getElementById('permeateTDS').value; var resultDisplay = document.getElementById('resultDisplay'); var rejectionResult = document.getElementById('rejectionResult'); var membraneStatus = document.getElementById('membraneStatus'); var removalAmount = document.getElementById('removalAmount'); // 2. Validate inputs // Ensure inputs are not empty and Feed TDS is greater than 0 to avoid division by zero if (feedTDS === "" || permeateTDS === "") { alert("Please enter both Feed TDS and Permeate TDS values."); return; } var feedVal = parseFloat(feedTDS); var permeateVal = parseFloat(permeateTDS); if (isNaN(feedVal) || isNaN(permeateVal)) { alert("Please enter valid numeric values."); return; } if (feedVal = feedVal) { alert("Permeate TDS must be lower than Feed TDS for a functioning RO system."); return; } // 3. Perform Calculation // Formula: ((Feed – Permeate) / Feed) * 100 var rejectionRate = ((feedVal – permeateVal) / feedVal) * 100; var tdsRemoved = feedVal – permeateVal; // 4. Update Result Display resultDisplay.style.display = "block"; rejectionResult.innerHTML = rejectionRate.toFixed(2) + "%"; // Update removal stats text removalAmount.innerHTML = "Total TDS Removed: " + tdsRemoved.toFixed(1) + " ppm"; // 5. Determine Status var statusText = ""; var statusClass = ""; if (rejectionRate >= 97) { statusText = "Status: Excellent Performance"; statusClass = "status-excellent"; } else if (rejectionRate >= 95) { statusText = "Status: Good Performance"; statusClass = "status-good"; } else if (rejectionRate >= 90) { statusText = "Status: Fair (Monitor Closely)"; statusClass = "status-fair"; } else { statusText = "Status: Poor (Replace Membrane)"; statusClass = "status-poor"; } // Reset classes membraneStatus.className = "ro-result-status " + statusClass; membraneStatus.innerHTML = statusText; }

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