Chlorine test strips can quickly tell you how much chlorine is in a sample of water, but sometimes, understanding these seemingly simple results can be tricky.
What Do Chlorine Test Strips Measure?
Most chlorine test strips measure either free chlorine or both free chlorine and total chlorine. The amount of free chlorine present tells you whether or not the water is safe to drink.
Difference between Total Chlorine and Free Chlorine
Most water treatment plants utilize chlorination, which involves adding chlorine to drinking water, as part of their disinfection process. When added in the right amounts, chlorine can effectively kill bacteria and prevent against future down-stream contamination.
During chlorination, chlorine is added to water and reacts with inorganic and organic materials to deactivate bacteria and kill microorganisms. The leftover chlorine that is not used to meet the chlorine demand is called total chlorine.
Total chlorine is made up of:
Free Chlorine: leftover chlorine that is ready to deactivate bacteria
Combined Chlorine: chlorine that has reacted with inorganic or organic molecules that can no longer deactivate bacteria. Your combined chlorine might include chloramine or disinfection byproducts called trihalomethanes.
Several trihalomethanes are carcinogenic. To know if your levels are higher than recommended drinking water standards you can test your water for total trihalomethanes in a certified lab.
What Is a Safe Amount of Chlorine in Drinking Water?
The optimal concentration of free chlorine residual is between 0.3 PPM and 0.5 PPM.
Levels from 0.2 PPM-4 PPM are considered acceptable.
What Does PPM Stand for on Chlorine Strips?
PPM means parts per million. This measurement is the mass of a chemical or contaminate per unit volume of water. PPM or mg/L (milligrams per liter) is the same thing.
What Is a Dangerous Amount of Chlorine in Drinking Water?
The EPA states that ingesting water with chlorine levels above 4 PPM can cause negative health impacts.
How To Use a Chlorine Test Strip
1. Remove the chlorine strip from the packet.
2. Run your water for about 5 minutes to clear pipes of any stagnant water.
Place the strip under a gentle stream of water for 10 seconds or fill a clean cup* with water and place the strip in the water for 30 seconds– using a gentle back-and-forth motion.
Do NOT dip chlorine strip into any sampling containers!
3. Compare the color of the free chlorine pad to the chart on your packet or instruction card.
4. The colors on the pads indicate chlorine concentration in PPM (parts per million).
5. Upload the results and photos to the "Self-Test" section of your report.
Read more about how to upload self-test strip results here.