Designing an industrial reverse osmosis system without checking feed water quality is the biggest mistake plant owners make. Borewell water, river water, and municipal supply all contain different levels of minerals, dirt, and chemical impurities.
If you ignore key parameters like Silica, Iron, Hardness, or SDI, your system will face rapid membrane choking, high electricity bills, and frequent maintenance costs.
Here is a simple, step-by-step guide to reading your water test report so you can select the right pre-treatment system and design an efficient RO plant.
1. Total Dissolved Solids (TDS) and Electrical Conductivity (EC)
What it means: TDS measures the total amount of dissolved minerals and salts in water, calculated in ppm (parts per million) or mg/L.
Impact on RO Design: High TDS requires higher pump pressure to push water through the RO membranes.
Selection Rules:
TDS up to 2,000 ppm: Standard low-energy brackish water RO system works smoothly under normal operating pressure.
TDS between 2,000 to 5,000 ppm: High-pressure pump is mandatory to overcome osmotic pressure.
TDS above 10,000 ppm: Requires specialized high-pressure seawater membrane design.
High TDS determines pump pressure and membrane capacity. Explore our standard Industrial RO Plant options built for different raw water TDS ranges.
2. Silt Density Index (SDI) and Turbidity
What it means: Turbidity measures water mudiness, while SDI measures fine suspended particles that can block membranes.
Safe Limits for RO:
Target SDI: Must be below 3.0 (Maximum limit is 5.0).
Target Turbidity: Must be below 1.0 NTU.
Pre-Treatment Fix: If your raw water has high mud or floating dirt, a basic sand filter is not enough. You must install a Multi-Media Filter (MMF) or an Ultrafiltration (UF) system before the RO unit.
3. Silica Levels
What it means: Silica is dissolved glass-like mineral present in ground water.
Impact on RO Design: Silica forms hard glass-like scaling on membranes that cannot be washed off with normal CIP cleaning chemicals.
Design Limits:
Silica below 20 ppm: Standard antiscalant chemical dosing is sufficient.
Silica between 20 to 100 ppm: Specialized high-silica antiscalant chemical dosing is required.
Silica above 100 ppm: Plant water recovery must be kept low (around 60% to 65%) to stop silica from settling on membranes.
4. Total Hardness and LSI Index
What it means: Hardness measures calcium and magnesium salts present in water that cause white scale build-up inside pipes and membranes.
Impact on RO Design: High hardness blocks the last stage membranes first, reducing clean water output drastically.
Pre-Treatment Fix:
If hardness is moderate, dose high-quality antiscalant chemical continuously.
If hardness is very high, installing an upstream Water Softener Plant removes hardness completely before water enters the RO plant.
5. Iron and Manganese
What it means: Dissolved heavy metals common in borewell water.
Impact on RO Design: Iron turns yellow/brown when mixed with air and sticks to membranes like a thick layer of rust.
Safe Limits:
Iron: Must be less than 0.05 ppm.
Manganese: Must be less than 0.02 ppm.
Pre-Treatment Fix: Install an Iron Removal Filter (Birm or Manganese Greensand filter) before the RO cartridge filters.
6. Free Chlorine
What it means: Disinfectant chemical added to municipal or raw water storage tanks to kill bacteria.
Impact on RO Design: Modern Polyamide RO membranes get permanently damaged if exposed to free chlorine above 0.1 ppm. Chlorine burns the membrane layer, causing high TDS output.
Pre-Treatment Fix: Install an Activated Carbon Filter (ACF) or dose Sodium Metabisulfite (SMBS) chemical to eliminate chlorine completely. Protecting your Industrial RO Membranes from chlorine is essential for long membrane life.
Quick Water Test Reference Table
| Raw Water Parameter | Safe Limit for RO Feed Water | Required Pre-Treatment System |
| Turbidity / Dirt | Less than 1.0 NTU | Multi-Media Filter / UF System |
| SDI (15 min) | Less than 3.0 | Coagulant Dosing / Dual Media Filter |
| Free Chlorine | Less than 0.1 ppm | Activated Carbon Filter / De-chlorination |
| Iron Content | Less than 0.05 ppm | Iron Removal Filter |
| Silica | Less than 20 ppm | High-Silica Antiscalant Dosing |
| Hardness | Low to Moderate | Antiscalant Dosing or Water Softener |
Key Takeaway for Plant Owners
A water test report is the master key for your water treatment project. Investing in the right pre-treatment filter saves you huge money on frequent membrane replacements, chemical cleaning downtime, and pump power consumption.
Want our engineers to review your site’s water test report? Contact us today to get a customized RO plant proposal.