READING FREE CHLORINE LEVELS
1. Let the cold water run for at least a minute to ensure fresh water for the reading.
2. Fill the left hand tube to at least the bottom of the frosted marking. Accuracy is not important except to be sure the level of water is high enough. This is the “blank”. Wipe off the outside of the tube if it is wet and replace it in the left slot of the black box.
3. Open a package of the reagent chemicals.
4. Rinse out the right hand tube then fill it to the bottom of the frosted portion and wipe off the outside of the tube. Accuracy is a little more important in this tube as the chemicals are measured for 5 ml of water. However, if you have a little more water in the tube you will still get an accurate reading as there is actually more than enough chemical in the packet to read 5 ml of water.
5. Add the chemicals to the tube and shake/swirl gently to dissolve, then replace the tube into the right hand slot of the black box.
6. Wait about 30 seconds to one minute after adding the chemical and take the reading.
a. Holding the box against a white background (a cloudy sky, for example), turn the wheel until the colours in the two openings match.
b. Confirm your reading by checking the colours at the line before and the line after the one you think matches.
7. Enter the reading into the book, noting the time to the nearest ¼ hour.
READING TOTAL CHLORINE LEVELS
Follow the same procedure, but use the packet of chemicals for Total Chlorine. Normally we only do this occasionally. See notes below.
Record the value for total chlorine.
ANALYSIS
Free Chlorine, otherwise known as Available Chlorine, is the chlorine remaining in the water (residual) that has not combined with material in the water, such as bacteria or other organic matter. Total Chlorine is exactly what the word implies. All the Chlorine, both residual and combined.
If Free and Total Chlorine are the same, it's an indication that there was very little organic material in the water for chlorine to combine with. This is another way of saying that there is none or little Combined (or used) Chlorine in the water. This is a good indication of the effectiveness of the filtration system and/or the clean quality of the source water.
Although this website is describing the process at a swimming pool, the chemistry is the same. As the article points out, Total Chlorine minus Free Chlorine = Combined Chlorine. Or this: FC + CC = TC
In our system, we aim for 0.6 ppm Free Chlorine at the reservoir. Chlorine levels will vary at different locations around the subdivision. For example, at the hydrant just uphill from the Treatment Site, we would expect to find approximately 1.0 ppm Free Chlorine. At the lower end of the subdivision, closer to the highway, we would expect to find approximately 0.3 ppm. Free Chlorine levels are tested at various times around the subdivision to detect any problems.
It is normal practice to test for Free Chlorine on a regular basis at the reservoir and at random times elsewhere. All tests results are recorded in a notebook kept in the Reservoir pump house.