Abstract
Regular monitoring of drinking water quality is vital to identify contamination of potable water supplies. Testing for microbial contamination is important to prevent transmission of waterborne disease, but establishing and maintaining a water quality monitoring programme requires sustained labour, consumables and resources. In low resource settings such as developing countries, this can prove difficult, but measuring microbial contamination is listed as a requirement of reaching the UN's Sustainable Development Goal 6 for water and sanitation. A nine-month water quality monitoring programme was conducted in rural Malawi to assess the suitability of tryptophan-like fluorescence (TLF), an emerging method for rapidly detecting microbial contamination, as a drinking water quality monitoring tool. TLF data was compared with thermotolerant coliforms (TTCs, E. coli) and inorganic hydrochemical parameters. A large (n = 235) temporal dataset was collected from five groundwater drinking water sources, with samples collected once or twice weekly depending on the season. The results show that TLF can indicate a broader contamination risk but is not as sensitive to short term variability when compared to other faecal indicators. This is likely due to a broad association of TLF with elevated DOC concentrations from a range of different sources. Elevated TLF may indicate preferential conditions for the persistence of TTCs and/or E. coli, but not necessarily a public health risk from microbial contamination. TLF is therefore a more precautionary risk indicator than microbial culturing techniques and could prove useful as a high-level screening tool for initial risk assessment. For widespread use of TLF to be successful, standardisation of TLF values associated with different levels of risk is required, however, this study highlights the difficulties of equating TLF thresholds to TTCs or E. coli data because of the influence of DOC/HLF on the TLF signal.
Highlights
Understanding temporal variability of drinking water quality in low and middle income (LMI) countries is vital to protect human health from transmission of waterborne disease and harmful concentrations of organic and inorganic contaminants
This study found the same, which indicates that the current detection limit of Tryptophan-like fluorescence (TLF) is currently approximately 10 cfu/100 mL for thermotolerant coliform (TTC) and 9.6 most probable number (MPN)/100 mL for E. coli
TLF offers a rapid assessment of water quality, as an earlywarning indicator, but cannot be related directly to public health risk from faecal contamination and usage is limited to high-level screening approaches
Summary
Understanding temporal variability of drinking water quality in low and middle income (LMI) countries is vital to protect human health from transmission of waterborne disease and harmful concentrations of organic and inorganic contaminants. In sub-Saharan Africa, millions of people rely on groundwater as a drinking water source, using handpumped boreholes or shallow wells (Bonsor et al, 2011; WHO and UNICEF, 2020). In the dry season especially, groundwater provides a lifeline as alternative sources such as seasonal streams, ponds and rainwater harvesting systems inevitably dry up (Kelly et al, 2018; MacDonald et al, 2019). Handpumped boreholes in sub-Saharan Africa have been shown to have low levels of microbial contamination (Lapworth et al, 2020). This is dependent on local hydrogeological conditions, which can vary seasonally (Kostyla et al, 2015; Lapworth et al, 2020)
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