Effectiveness of free residual chlorine test kit for screening test of nitrite in drinking water

Abstract

The quantification of nitrite (NO₂^-) in drinking water is very important because it affects the health of consumers. As a result, the Department of Health (DOH) included nitrite testing in the DOH’s criteria for drinking water quality published in 2020 and recommended using chlorine as disinfectant for drinking water quality processes. Moreover, DOH suggests to use the free residual chlorine test kit as        a tool for self-screening test of drinking water quality due to easy, not complex processes, cheap and not required expensive instruments. Consequently, the free residual chlorine test kits have been used extensively. The previous studies showed that chlorine in drinking water reduces the amount of nitrite. This cross-sectional study aims to identify the effectiveness of free residual chlorine test kit for self-screening test of free residual chlorine in drinking water by comparison with the standard method, and determine the effectiveness of free residual chlorine test kit for screening test of nitrite. Overall, the 360 drinking water samples were collected and screened for free residual chlorine by using a test kit, and also were analyzed for free residual chlorine and nitrite by standard method. The descriptive statistics were used to describe the characteristics of the drinking water samples and using the Wilcoxon Signed Ranks test to compare the difference between the two groups of samples that were not independent of each other.  Results showed that 104 drinking water samples (28.9%) were found free of residual chlorine at a concentration ranging from 0 to 13.5 mg/L and 31 drinking water samples (8.6%) were found nitrite at a concentration between 0 and 0.4 mg/L. The effectiveness of the test kit for self-screening of free residual chlorine compared with standard methods were 100% sensitivity, 96.4% specificity, 92.0% positive predictive value, 100% negative predictive value, and 97.5% accuracy. As expected, of 110 drinking water samples with positive of free residual chlorine >0.2 mg/L using a standard color chart were not detected the amount of nitrite. Therefore, the test kit can be used as a preliminary test prior to nitrite analysis with standard method, it will save costs up to 29.8% of the nitrite analysis. In conclusion, self-screening of free residual chlorine in drinking water by the test kit is very accurate. It is effective for using as a preliminary test prior to nitrite analysis which the public can use as a practical guideline. This will save costs for testing the drinking water quality.