Chloramine is a disinfectant that water systems use to keep a lasting residual in the pipes after treatment. It forms when chlorine and ammonia are combined, so it stays in the distribution network longer than free chlorine does. Some homes in St. Charles County receive water that contains chloramine, and homeowners often learn this only when a home test gives a reading that does not match what they expected.
This guide covers one practical question: how to check for chloramine at home using a chlorine test kit, and how to read the results without guessing.
Why a standard chlorine reading can mislead
Many simple test kits report two numbers. Free chlorine is the chlorine that is available to react right away. Total chlorine includes the free chlorine plus the chlorine already bound to other compounds, such as the ammonia in chloramine. The gap between the two readings is called combined chlorine. When your total reading is clearly higher than your free reading, the water likely contains chloramine or another combined form.
A kit that reports only free chlorine may show a low or zero result on water that is still disinfected. A homeowner who checks only free chlorine could wrongly conclude the water has no disinfectant at all, when the disinfectant is simply in a different form.
What you need before you test
- A test kit that reports both free and total chlorine, usually one that uses the DPD method with a color chart
- Clean test vials, rinsed with tap water rather than soap, since soap residue can throw off results
- A cool, shaded spot to read the colors, because light and heat can change how they look
- A notebook or phone note with the date, the tap you used, and both readings
Step by step
- Run the cold kitchen tap for a minute or two so the water in the line is fresh.
- Fill a vial to the line the kit specifies, keeping the inside of the vial and the cap clean.
- Add the free chlorine reagent, cap the vial, and mix gently as the instructions describe.
- Read the color against the chart within the time window the instructions give.
- Repeat with a second vial using the total chlorine reagent.
- Write down both results, then subtract the free reading from the total reading to find the combined amount.
Reading the difference
If the two readings are close, your water is probably carrying mostly free chlorine. If the total reading is well above the free reading, you have combined chlorine, and chloramine is a common source of that in municipal supplies. Keep in mind that a home kit is a screening tool. It tells you what to ask next, not the exact makeup of the water.
Test in more than one place
Because your water enters through the service line, a reading at the tap nearest the main is the most useful baseline. Water heaters, softeners, carbon filters, and older plumbing can all change what you see at other taps. Test at the nearest tap, then at a tap farther from the entry point, and compare the results. If you have a softener or filter, test before and after it so you can see whether the equipment changes the reading.
When to involve a lab
A home kit cannot answer every question. If you need documented results for a rental, a pet or aquarium setup, or a dispute, a certified laboratory can run a formal test. Ask the lab which parameters it reports and what sample bottles it requires. You can also review the annual water quality report published by your water provider for St. Charles County. That report lists the disinfectant in use and summarizes the residual levels measured in the system.
Pets and aquariums
Chloramine is one reason aquarium owners test their water before filling a tank, and people who keep fish, reptiles, or amphibians often want to know exactly what comes out of the tap. A conditioner made for aquarium use is one option people consider. A veterinarian or aquarium specialist can advise you on what your animals need and how to prepare their water.
Next steps
- Record your free and total readings at two taps on different days
- Check your provider's annual report to confirm which disinfectant it lists
- Test again after any change to your water heater, softener, or filter
- Contact a certified laboratory if you need results you can document