December 2022

What sampling frequency is required to reliably indicate fecal contamination of groundwater? 

Technical Brief: Variability of Microbial Contamination in Groundwater and Optimal Sampling Frequency: Evidence from Rural Uganda.

Background

Drinking water contaminated with fecal contamination can result in diarrhea and other illnesses, particularly in children. E. coli is commonly measured as an indicator of fecal contamination. Higher levels of fecal contamination are associated with higher risk of illness [1].

Temporal variability of fecal contamination in drinking water sources is common. Source water quality often varies across seasons (e.g., wet season and dry season) and in response to specific events (e.g., rainfall) [2,3]. For groundwater, rainfall and seasonal variation may affect individual aquifers differently: some aquifers experience a dilution effect (i.e., decreased concentration of pollutants), and others experience a concentrating effect (i.e., increased concentration of pollutants) in response to increased rainfall and rise in groundwater levels [3]

Despite potential temporal variability, sampling of groundwater sources in Sub-Saharan Africa is often infrequent. For example, Multiple Indicator Cluster Surveys (MICS) provide one-off sampling of water sources [1] and the WHO Guidelines for Drinking Water Quality recommend sampling and testing for E. coli every 3-5 years for point sources (e.g., handpumps and springs) [4].

This may be insufficient to estimate the risk associated with drinking water from sources with high variability throughout the year. However, as increased sampling frequency requires increased cost and resources, it is important to understand the minimum frequency of monitoring required for different applications.

Additionally, most prior research focused on seasonal variability, and better understanding water quality variability over shorter time scales would be helpful to inform monitoring recommendations. Prior research provided recommendations related to sampling frequency for regulatory compliance of piped systems in sub-Saharan Africa [5]; our goal is to consider recommendations for non-piped systems based on different stakeholder needs. 

Summary of Key Findings

With funding from the Conrad N. Hilton Foundation, The Aquaya Institute (Aquaya) supports government agencies in selected districts of Ghana and Uganda in their efforts to achieve 100% coverage of safe, sustainable, and equitable drinking water supplies. 

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