Chlorine is one of those minerals that are good for drinking water, but just like any other chemical, moderate levels are needed. The presence of free chlorine in drinking water could indicate two things:
That enough chlorine was added to the water to kill all the harmful pathogens and,
The water was protected from getting contaminated during storage.
So much so, testing is done to conduct dosage testing in project areas that are yet to start the chlorination process. And the second reason is to monitor the chlorination projects to ensure they are compliant. The safe level of chlorine in the water that is safe to drink is 4ppm, parts per million. You also have to realize that there are twokinds of chlorine, free and total chlorine.
Here is how tap water is tested for chlorine:
Using testing stripes
Fill your flask or glass with a 20mL sample of tap water. Before filling the glass, please turn on the faucet and let it run for a few seconds. Now, dip a Residual Chlorine Test Strip into the water and move it back and forth for 5 seconds at a rate of 2 times per second. Remove the test strip and compare it to the color chart that came with it. You then compare the water's color change against the stripe that indicates the amount of chlorine in the water.
Using the color wheel
In the presence of chlorine, color wheel test kits employ the powder or tablet chemical DPD (N, N diethyl-p-phenylenediamine), which produces a color change to pink. Because the person testing uses a color wheel to manually correlate the color to a quantitative free or total chlorine reading, color wheels are more accessible and less costly than electronic devices for measuring the intensity of the color change.
The good thing about using this test is that it is readily available, and the results are instant. They are also accurate if used properly. On the flip side, this test lacks standardization.
Using Digital Colorimeters
In emerging nations, digital colourimeters are the most accurate tool to assess free and total chlorine residuals in tap water. The approach used by these colourimeters is as follows:
1) putting DPD tablets or powder into a container of sample tap water, which causes a pink color change;
2) putting the vial into a meter, which reads the intensity of the color change by producing a spectrum of light and electronically calculating and presenting the color intensity.
The meter's ranking is 0 to 4 mg/L, or 0 to 4 parts per million (parts per million).
When chlorine is in low doses, it simply means that that water is not well sanitized. This means that when you drink it, you may become sick because of the viruses and bacteria present. On the flip side, when the chlorine is too much, it can cause stomach disturbances like vomiting, diarrhoea, and long-term bladder cancer. And this is why one should opt to get the water tested or, to be on the safe side, perhaps use a carbon water filtration system to keep the chlorine levels below 99%.
You can also read more about how to test your water at home for everything else.