Guest Column - October 2018
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Healthy Swimming Pools & the Importance of Chlorine

By Chad Howard, M.D.

Anything to decrease the demand for chlorine is helpful in this situation, such as supplementing disinfection with UV sterilization, rinsing off before entering the water and maintaining proper pH levels. The most important controllable variables when it comes to disinfection byproduct formation are the free chlorine concentration and the amount of organic matter coming from bathers.

The Model Aquatic Health Code (MAHC), developed in conjunction with the Centers for Disease Control, provides guidance for state and local authorities to make recreational water use safer. It's based on science and best practices and updated periodically.

From those guidelines, the target chlorine level is a minimum of 1 ppm for swimming pools not using cyanuric acid. For those using cyanuric acid, the minimum recommended chlorine level is 2 ppm, and 3 ppm for venues that pose more of a sanitization challenge, such as hot tubs. For any location the level shouldn't exceed 10 ppm when swimmers are present. Guidelines for bromine are a little different, with 3 ppm in aquatic venues other than hot tubs and spas, where 4 ppm is the minimum.

Chlorine's sanitizing power actually peaks at a pH of 5.5, but the MAHC recommends a pH between 7.2 and 7.8 to avoid skin and mucous membrane irritation. A calcium hardness level of 150 to 400 ppm is recommended. Cyanuric acid as a stabilizer or conditioner should be kept under the MAHC max of 90 ppm, and most experts recommend keeping it between 30 and 50 ppm. Higher levels may cause too much chlorine binding and result in "chlorine lock," rendering the chlorine ineffective.

It's crucial to have accurate testing equipment to verify the proper water chemistry and disinfectant levels. In facilities that rely on controllers to maintain the desired water parameters, the use of photometers/colorimeters is the most accurate method to verify system performance. As part of the MAHC, Water Quality Testing Devices (WQTD) must meet NSF/ANSI 50 standards. The current standards for WQTDs specify accuracy and precision requirements for chlorine, pH and other critical water parameters. Certified products are given an accuracy rating to one of three levels: L1, L2 or L3, with L1 (Level 1) being the most accurate. Whenever possible select a test kit with Level 1 accuracy to best ensure bather safety.

Dr. Chad Howard, M.D., is the Principal Medical Writer with Industrial Test Systems, Inc.