A DIY reverse osmosis system can be assembled and tested at home with just a few key components. This guide explains how to hook up the membrane, test your system’s water quality, and understand what your TDS (Total Dissolved Solids) readings really mean — ensuring your RO system is working efficiently.

Step 1: Review Your System Setup

Before testing, ensure your RO unit is properly connected. If you haven’t seen how to build the system, start with Part 1 of our DIY Reverse Osmosis System Guide.
 For this test, the only additional component used is a diverter valve that attaches directly to the faucet — perfect for connecting your setup without permanent plumbing.
 → View the diverter valve used in this test.

Step 2: Run and Flush the System

While professional installations use a storage tank for complete flushing, a quick test run is enough to confirm performance.

  1. Turn on the water and let it run for several minutes.

  2. Observe the water flow from the waste and purified lines.

  3. Check for leaks around fittings and connections.

Flushing removes manufacturing preservatives and primes the RO membrane for consistent filtration.

Step 3: Measure Water Quality with a TDS Meter

Reverse osmosis systems are evaluated based on TDS reduction, which measures dissolved minerals and salts in water (in parts per million or ppm).
 Use a TDS meter to compare readings before and after filtration.
 → Shop the HM Digital TDS-EZ Meter here.

Example:

  • Tap water: 100 ppm

  • RO water: 3–8 ppm

This shows a rejection rate of 92–97%, which is excellent for most home systems.

Step 4: Understand RO Membrane Rejection Rates

Each RO membrane includes a specification sheet showing its rejection rate — the percentage of impurities it removes under ideal conditions.
 For instance, a Filmtec membrane offers a 97% rejection rate at 77°F, 8.0 pH, 15% recovery, and 500 ppm feed water. Real-world conditions vary, so achieving 92–97% is perfectly normal.

If your readings fall slightly below the listed spec, check for:

  • Cold feed water (reduces efficiency)

  • High TDS input (reduces rejection percentage)

  • Membrane age or improper flushing

Step 5: Interpreting TDS Readings Correctly

TDS meters measure charged ions only — they don’t account for uncharged particles or organic matter.
 For unknown water sources or well water, consider a complete water analysis to determine if pre-treatment or post-treatment (such as carbon filters or UV purification) is necessary.

Learn more about why RO systems improve your household water quality in our related post:
Top Benefits of Installing a Reverse Osmosis System in Your Home

For additional insights into system performance and environmental standards, visit the EPA’s guide on Point-of-Use Reverse Osmosis Systems.

Quick Tips for Best Results

  • Always flush new membranes before testing.

  • Use room-temperature water for accurate readings.

  • Recheck TDS after several hours of operation for stabilized results.

  • Replace pre-filters every 6–12 months to maintain rejection rates.



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