Household effectiveness vs. laboratory efficacy of point-of-use chlorination

Abstract

Treatment of water at the household level offers a promising approach to combat the global burden of diarrheal diseases. In particular, chlorination of drinking water has been a widely promoted strategy due to persistence of residual chlorine after initial treatment. However, the degree to which chlorination can reduce microbial levels in a controlled setting (efficacy) or in a household setting (effectiveness) can vary as a function of chlorine characteristics, source water characteristics, and household conditions. To gain more understanding of these factors, we carried out an observational study within households in rural communities of northern coastal Ecuador. We found that the efficacy of chlorine treatment under controlled conditions was significantly better than its effectiveness when evaluated both by ability to meet microbiological safety standards and by log reductions. Water treated with chlorine achieved levels of microbial contamination considered safe for human consumption after 24 hours of storage in the household only 39 – 51% of the time, depending on chlorine treatment regimen. Chlorine treatment would not be considered protective against diarrheal disease according to WHO log reduction standards. Factors that explain the observed compromised effectiveness include: source water turbidity, source water baseline contamination levels, and in-home contamination. Water in 38% of the households that had low turbidity source water (< 10 NTU) met the safe water standard as compared with only 17% of the households that had high turbidity source water (> 10 NTU). A 10 MPN/100mL increase in baseline E. coli levels was associated with a 2.2% increase in failure to meet the E. colistandard. Higher mean microbial contamination levels in 54% of household samples in comparison to their matched controls, which is likely the result of in-home contamination during storage. Container characteristics (size of the container mouth) did not influence chlorine effectiveness. We found no significant differences between chlorine treatment regimens in ability to meet the safe water standards or in overall log reductions, although chlorine dosage did modify the effect of source conditions. These results underscore the importance of measuring both source water and household conditions to determine appropriate chlorine levels, as well as to evaluate the appropriateness of chlorine treatment and other point-of-use water quality improvement interventions.

Measuring household consumption and waste in unmetered, intermittent piped water systems

“…In comparison, a study in Ecuador (Levy et al, 2014) found that 48.8e61.3% of samples collected from storage containers with chlorinated water had detectable levels of E. coli. Chlorinated water should have lower contamination levels due to its residual disinfection capacity, but there may have been higher prevalence of E. coli in the source water or higher risks of recontamination in the Ecuador study.…”

Chlorination of Household Drinking Water Among Cholera Patients' Households to Prevent Transmission of Toxigenic Vibrio cholerae in Dhaka, Bangladesh: CHoBI7 Trial

“…Previous studies have shown that high turbidity can affect free available chlorine in drinking. 17 Therefore, to ensure that our experiments were representative of the drinking water source used by the majority of households in Dhaka city, we prepared chlorine stock solutions using Dhaka Water Supply and Sewerage Authority (DWASA) water. The DWASA water used for laboratory experiments had a turbidity of < 1 NTU, a pH of 7.2, and free available chlorine concentration below the detection limit (< 0.01 mg/L).…”

“…14,16 However, previous studies have also found that the effectiveness of chlorine in reducing microbial contamination can vary based on source-water turbidity, source-water baseline contamination levels, and in-home contamination. 16,17 In rural Ecuador, only 17% of households with high source-water turbidity (> 10 NTU) were able to achieve the World Health Organization guideline for safe drinking water after chlorine treatment with a sodium hypochlorite (NaOCl) solution of 1.875 mg/L. 17 In alignment with this finding, a study which analyzed water samples collected from 13 African countries recommended a dosage of 1.875 mg/L NaOCl for water sources with an NTU less than 10, and 3.75 mg/L for water sources between 10 and 100 NTU to meet a free available chlorine concentration greater than 0.2 mg/L after 24 hours of storage.…”

“…16,17 In rural Ecuador, only 17% of households with high source-water turbidity (> 10 NTU) were able to achieve the World Health Organization guideline for safe drinking water after chlorine treatment with a sodium hypochlorite (NaOCl) solution of 1.875 mg/L. 17 In alignment with this finding, a study which analyzed water samples collected from 13 African countries recommended a dosage of 1.875 mg/L NaOCl for water sources with an NTU less than 10, and 3.75 mg/L for water sources between 10 and 100 NTU to meet a free available chlorine concentration greater than 0.2 mg/L after 24 hours of storage. 16 Therefore, the chlorine concentration needed to deactivate pathogens in drinking water varies by setting and is based on source-water quality parameters and household drinking water storage and use practices.…”

Household Water Treatment Technologies For Microbial Removal in Kabale District, Southwestern Uganda

“…When the same households were provided PUR, it was noted that 33% had Escherichia coli concentrations < 1 CFU/100 ml, and when provided filters, 39% had Escherichia coli < 1 CFU/100 ml (Albert, Luoto, & Levine, 2010).In this study, the performance of both aqua safe tablets and application WaterGuard tablets in removing total coliforms from KMS1sample was slightly lower compared to other samples, probably because of much higher turbidity observed. The physical-chemical properties of source water have been observed to limit bacterial reduction application of aqua safe tablets (Levy et al, 2014;Mohamed et al, 2015). Turbidity is known to negatively affect water disinfection by chlorine (Mohamed et al, 2015) by exerting chlorine demand.…”