What are expert tips for testing your water after treatment?

A TDS meter is the best $15 investment for RO system owners. A quick reading tells you instantly if the membrane is still performing. Test first thing in the morning (first-draw water) for the most revealing results -- contaminants concentrate in standing water overnight. Keep a log of test results over time. Trends are more informative than single readings. If you're on a well, test for bacteria (coliform) at least annually. Treatment systems can mask bacterial issues if they fail.

What mistakes should I avoid with testing your water after treatment?

Never testing and assuming the system works because the water tastes fine. Many contaminants are tasteless and odorless. Only testing the treated water. Without a baseline (untreated) reading, you can't calculate removal efficiency. Using expired test strips -- they give inaccurate results. Check the expiration date. Testing immediately after a filter change. Run water for a few minutes first to flush carbon fines and manufacturing residues.

Testing Your Water After Treatment

Maintenance Guide Easy 5-15 minutes for home tests $10-$50 for test kits / $30-$150 for lab tests

Created by Ryan Pietrzak Illinois Licensed Plumber · In the plumbing industry since 2009

Updated February 20, 2026

Key Takeaway

You installed a water treatment system to fix a problem. But how do you know it's actually working? The water might taste fine, look clear, and smell normal -- while the system has been exhausted for months and contaminants are passing right through. Testing is the only way to verify. It takes 5 minutes with a home kit or a mail-in sample for comprehensive results.

Overview

What to Know

What to Test and When

Test the specific contaminants your system targets. If you have a softener, test hardness monthly. RO system? Test TDS (total dissolved solids) quarterly. Carbon filter for chlorine? Test chlorine levels after filter changes. Iron filter? Test iron levels quarterly. Test both before (untreated water) and after (treated water) to see the difference.

Home Test Kits

TDS meters ($10-$20) give instant total dissolved solids readings -- perfect for RO systems. Test strips ($10-$15 for a pack) cover hardness, pH, chlorine, iron, and more. Liquid reagent kits ($15-$30) are more accurate than strips for specific tests like hardness and iron. Digital pH meters ($15-$25) are the most accurate for pH testing.

Lab Testing

For comprehensive analysis, send a sample to a certified lab. Tap Score and National Testing Laboratories offer mail-in kits ($30-$150 depending on the panel). Lab tests cover heavy metals, bacteria, VOCs, PFAS, and dozens of other contaminants that home kits can't detect. Worth doing annually, especially on well water.

Interpreting Results

Compare treated water results to EPA maximum contaminant levels (MCLs) and your system's rated performance. An RO system should reduce TDS by 90-98%. A softener should bring hardness below 1 GPG. A carbon filter should reduce chlorine to near zero. If results aren't meeting these benchmarks, something needs attention -- filter change, system maintenance, or a bigger issue.

Pro Tips

A TDS meter is the best $15 investment for RO system owners. A quick reading tells you instantly if the membrane is still performing.
Test first thing in the morning (first-draw water) for the most revealing results -- contaminants concentrate in standing water overnight.
Keep a log of test results over time. Trends are more informative than single readings.
If you're on a well, test for bacteria (coliform) at least annually. Treatment systems can mask bacterial issues if they fail.

Mistakes to Avoid

Never testing and assuming the system works because the water tastes fine. Many contaminants are tasteless and odorless.
Only testing the treated water. Without a baseline (untreated) reading, you can't calculate removal efficiency.
Using expired test strips -- they give inaccurate results. Check the expiration date.
Testing immediately after a filter change. Run water for a few minutes first to flush carbon fines and manufacturing residues.

When to Call a Pro

If your test results show contaminants above EPA limits despite a properly maintained treatment system, consult a water treatment specialist. The system may be undersized, the wrong type for your specific contaminants, or there may be a plumbing issue allowing untreated water to bypass the system.

Bottom Line

Test what your system is supposed to remove, compare before and after, and do it on a schedule. A $10 TDS meter or $15 test strip pack tells you in seconds whether your treatment system is earning its keep or just taking up space.