September 18 is World Water Monitoring Day, an initiative designed to inspire people around the world to educate themselves about their local water quality and encourage action to protect water sources. Over the last few months, we’ve featured how Cleveland Water’s monitoring buoys in Lake Erie and sondes in our water intakes continuously monitor source water conditions.
Today, we’ll look at one of the water quality parameters we measure on land to ensure we’re delivering clean and safe drinking water to your tap: chlorine.
Cleveland Water has been using chlorine to disinfect the water since 1911. It’s one of the most important chemicals we use. Chlorine is added during the final step of the treatment process. Once added, the finished water is held in a reservoir so the chlorine has sufficient time to kill all bacteria and viruses.
At the plants, we monitor various chlorine parameters including how much we add, how much is needed to react with and neutralize any metals and organic compounds in the water, and the amount of chlorine remaining in the water that is still available for disinfection while the water is pumped throughout the distribution system. This remaining amount is called chlorine residuals.
Understanding the proper dose of chlorine to add during water treatment can be challenging because chlorine naturally dissipates over time and even faster in warm water. Factors like the volume of water being treated and the quality of water being taken in from Lake Erie all play a role. This is why our staff are experts at predicting how much water our customers will use based on the time of year and the day of the week. They’re also experts at knowing what the chlorine demand of the water will be based on source water quality and the season.
Cleveland Water takes 350 chlorine residual samples throughout the distribution system each month to ensure your water is safe. Samples are taken at the same locations so the results can be compared over time. Our goal is for each test location to have consistent chlorine residuals from week to week and season to season and to ensure residual levels are high enough to protect water all the way to your tap.
The Safe Drinking Water Act require that low levels of chlorine residuals be present in water as it is pumped throughout our distribution system. The range of allowable levels of chlorine residuals in water is between 4 parts per million (ppm) and to 0.2 ppm.
At Cleveland Water, our goal is to maintain chlorine residuals at a compliant level that both reduces the potential formation of by-products while keeping the water safe to drink. For 2017, our detections ranged from 1.03 to 1.22 ppm and were consistent per location. Consistent levels mean that our customers generally don’t notice a strong chlorine smell or taste.
However, some people’s noses are “experts” at detecting chlorine residual changes as small as 0.10 ppm. Sensitivity to the smell can also be impacted by hormones and medication. If you have an expert nose and notice a slight chlorine smell in your water, simply set the glass on the counter for a few hours and the chlorine will dissipate. If you have questions about your water, please call our Water Quality Line at 216-644-2639.