Abstract
Faecally-contaminated drinking water is a risk to human health, with the greatest risks to those living in developing countries. UN Sustainable Development Goal 6 aims to address this issue. Tryptophan-like fluorescence (TLF) shows potential as a rapid method for detecting microbial contamination in drinking water, which could reduce the spread of waterborne diseases. This study is the first to investigate the effectiveness of TLF for a large-scale survey using a randomised, spot-sampling approach. The large-scale survey took place in Malawi, sub-Saharan Africa, in the dry season (n = 183). A subset of sources were revisited at the end of the following wet season (n = 41). The effectiveness of TLF was assessed by comparing TLF results to thermotolerant coliforms (TTC), humic-like fluorescence (HLF), inorganic hydrochemical data and sanitary risk scores. The most prominent differences in microbial water quality were observed between source types, with little variation between districts and seasons. TLF, TTCs, turbidity and sanitary risk scores were all elevated at alternative sources (shallow wells and tap stands) compared to hand-pumped boreholes. In the dry season, 18% of hand-pumped boreholes showed TTC contamination, which increase to 21% in the wet season. Groundwater recharge processes are likely responsible for seasonal variability of inorganic hydrochemistry at hand-pumped boreholes. TLF was able to distinguish no and low WHO risk classes (TTC 0–9 cfu/100 mL) from medium, high and very high risk classes (TTC 10 – >1000 cfu/100 mL). TLF failed to distinguish between no and low risk classes, which limits the use of TLF for assessing water quality to drinking water standards. This dataset indicates that HLF may raise baseline TLF for samples with low TLF values, increasing false positives. Therefore, TLF is better suited as a rapid high-level water quality screening tool to assess moderate and high levels of faecal contamination.
Highlights
At least 2 billion people worldwide drink from faecally-contaminated water sources (WHO, 2018)
A small range of humic-like fluorescence (HLF) is observed across the dataset, indicating Tryptophan-like fluorescence (TLF) peaks were not influenced by HLF in this study, with the exception of two data points in the wet season (Fig. 3)
TLF, thermotolerant coliforms (TTCs), turbidity and sanitary risk scores were all elevated at alternative sources, in agreement with other studies that shallow groundwater sources are more vulnerable to contamination and in particular, open shallow wells (Lavoie and Viens, 1983; Lloyd and Bartram, 1991; Parker et al, 2010; MacDonald et al, 2019)
Summary
At least 2 billion people worldwide drink from faecally-contaminated water sources (WHO, 2018). This resulted in approximately 1.31 million deaths from diarrhoeal diseases in 2015, which could have been broadly preventable with adequate water, sanitation, hygiene and healthcare facilities (Troeger et al, 2017; Pruss-Ustun et al, 2014). The majority of these deaths occurred in low and middle income countries (LMICs) and 38% were children under 5 years old (Troeger et al, 2017; Pruss-Ustun et al, 2014). The JMP assessment method for SDG 6 states access to “improved water sources that are free from contamination” as a specific service level target (WHO and UNICEF, 2018)
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