How to Test for Chlorine in Tap Water (Free vs Total, and What Your Number Means)

To test tap water for chlorine, use a drinking-water chlorine test strip or a DPD drop kit on fresh cold water, and get one that reads both free and total chlorine. The two numbers together point to whether your city uses chlorine or chloramine, and that decides which carbon filter works. Treated tap water usually carries 0.2 to 1 ppm of chlorine, and up to 4 ppm is considered safe to drink.

My own house is on chlorinated water with a carbon filter on it. When city callers ask me where to start, I send them to the plumbing aisle at the hardware store for strips and ask them to text me the numbers. Below is which test to buy, how to run it, and what your number means.

Which chlorine test should you use?

For city water, a $19 pack of strips that reads free and total chlorine tells you what you have. For pools, CDC says a DPD kit gives the most accurate result and strips are less accurate. At a kitchen tap, either one tells you whether chlorine is there and roughly how much.

Chlorine is a test you run at the tap: Hach's method says a chlorine sample must be analyzed immediately and cannot be preserved for later analysis.

On a private well, there is no chlorine unless the well was shock chlorinated or has a chlorinator. After a shock, CDC says to run the faucets until the chlorine odor disappears; the same drinking-water strip tells you when it is gone. The full procedure is in how to shock chlorinate your well.

How to test tap water with a strip

A strip test takes a clean glass, cold tap water and the color chart on the bottle.

1. Run the cold tap first. Hach's method says to let a faucet run at least 5 minutes first, so the water in the glass is fresh and not water that sat in your pipes.
2. Fill a clean glass and test right away. Chlorine leaves water that stands, and Hach's method says to test as soon as you collect it.
3. Dip the strip for the time on the bottle. Precision Laboratories' strip, for one, is moved back and forth in the water for 5 seconds.
4. Match the color inside the time the bottle gives. The Precision strip gives you 5 minutes.
5. Write down both numbers. If your strips read free and total, you need the pair for the next step.

How to test with a DPD drop kit

A DPD drop kit turns the water pink. You match the pink to the kit's color chart. It is the chemistry the rules allow utilities to use: EPA lists DPD colorimetric as an approved method for free and total chlorine and lets states approve DPD test kits.

1. Fill the tube to the line with cold tap water from a tap that has run.
2. Add the free chlorine reagent and swirl. Pink means chlorine.
3. Read the free result within 1 minute. Hach's method says chloramine slowly pushes the free reading higher after that.
4. Run total chlorine with its own reagent. Hach's total method waits 3 minutes, then reads within the next 3.
5. Subtract free from total. The difference is combined chlorine, explained in the next section.

Use a clean tube for the free test. Hach warns that a trace of the total reagent left in the tube makes chloramine show up in the free reading. A digital meter runs the same DPD chemistry and shows a number instead of a color: Hanna's HI701 reads free chlorine from 0.00 to 2.50 ppm.

Free vs total chlorine

Free chlorine is the chlorine still working to kill germs. Total chlorine is that plus any chloramine. CDC puts it as a formula: total chlorine minus free chlorine = combined chlorine.

Many utilities make chloramine on purpose by adding ammonia to chlorine, and more than one in five Americans drink water treated with it, according to EPA. A free-only strip leaves chloramine out, so on chloraminated water it reads low. That is why you want the pair.

For more on the second row, see how to test for chloramine in tap water and chloramine vs chlorine.

Your water report says which chlorine you have

Every year your utility sends a water quality report, and CDC says it shows whether your water has a disinfectant, which kind, and the levels. The report sums up the utility's samples from across its system; your strip reads your own tap on one day. Here is how to read your water quality report.

What your chlorine number means

Treated city water usually has 0.2 to 1 ppm of chlorine. Up to 4 ppm is considered safe to drink. WHO gives the typical range for disinfected water; CDC gives the safe level. A ppm is the same as a milligram per liter (mg/L).

Whether chlorine at these levels is bad for you has its own page: is chlorine in water bad for you.

Why the chlorine smell got stronger

A stronger smell can mean your utility switched from chloramine to chlorine for a while. CDC says utilities do this to clear slime from the pipes, and the water utility in Palm Beach County, Florida, for one, switches every year and tells customers the smell may get stronger. A free and total pair shows it: during the switch, the free reading climbs up toward the total. Call your utility and ask before you change anything at home.

Got both chlorine numbers?

Text Aidan your two test numbers

Send both numbers and the size of your household. I'll tell you whether you need a filter, and which carbon fits.

Text Aidan443-277-2204 Call800-460-5810Aidan

8 AM to 5 PM Eastern, seven days a week. A real person, not a call center.

What removes chlorine after you test

Any carbon filter removes chlorine. Chloramine needs a special kind called catalytic carbon. Chloramine breaks down on carbon more slowly than chlorine does. Every carbon tank we sell holds Centaur catalytic carbon, which Calgon Carbon makes from bituminous coal for chloramine removal.

The 2.5 cubic foot non-backwashing tank is the one I recommend most; it needs no drain and no electricity. All of them are on one page under whole-house chlorine filters, and the best whole-house water filter for chlorine compares them. Once a filter is in, a strip at a tap after it tells you whether the carbon is still taking the chlorine out. I tell people to change the carbon about every 5 years.

Frequently asked questions