Chlorine in freshwater

What is chlorine?

Chlorine, on it’s own, is a greenish-yellow, highly reactive and diatomic gas that is almost never found free in nature by itself. When found in freshwater, chlorine is most often found bonded to other elements and ions. Most chlorine is commercially produced and is most widely known for being used within compounds to purify water/ create cleaning products.

A woman tests chlorine in freshwater using a Water Rangers testkit. She is comparing a test strip to the reference scale on the back of the bottle.

Why is chlorine important in freshwater?

We use chlorine to disinfect public water supplies from pathogens, such as bacteria and viruses. To have healthy drinking water supply in cities, chlorine acts as an important part of the cleaning process. Chlorine is used in water treatment plants, our water distribution systems, in supply reservoirs, including cisterns. It follows that we sometimes find leftover traces of chlorine from water treatment in our freshwater systems including lakes, rivers, and streams. Learn more about how chlorine is used to make our water safe to drink.

Remember — all the water that comes out of your tap, as well as down your drain, comes from a water source and eventually finds its way back.

What does a chlorine measurement mean?

Chlorine helps make our water drinkable! You likely will only find small traces of chlorine in most freshwater systems.

If you read your test results and note levels of chlorine in your water, you may be near a water treatment plant, or close to someone dumping pool water. Runoff from common domestic water uses, such as watering gardens, car washing, swimming pool draining, and driveway or road flushing, can all carry chlorine some distance, and end up in our lakes, rivers, and streams.

Water Rangers protocol for measuring chlorine in freshwater

For this test we use Taylor Pool and Spa Test Strips. Find out why we use this brand.

Pro-Tip: If the colour on the test strip appears in the middle of two colours on the bottle, you can record the absolute middle (for example, if the colour is somewhere between 2 and 3 the recorded have a value of 2.5).

Test for chlorine using these products:

Need a more precise chlorine test?

We recommend the Hanna Checker handheld chlorine meter, available from Amazon.