Comment on "On-site sanitation systems and fecal contamination in shallow groundwater in urban Indonesia: assessing influence of distance and rainfall variables" By G. L. Putri, A. M. Ilmi, R. Handayani, D. Iskandar, C. R. Priadi, J. Willetts, T. Foster; Water Research Volume 287 (Part B), 20 August 2025, 124431.

Putri et al. (2025) presented a rigorous study on fecal contamination of shallow groundwater from on-site sanitation systems (OSS) in urban Indonesia, examining how lateral and vertical distances and rainfall influence contamination risk. We commend their work and suggest five practical additions to further strengthen the evidence and actionability of their findings. Specifically, we recommend incorporating human-specific microbial source tracking (e.g., crAssphage) with transparent qPCR/dPCR reporting, and complementary chemical fingerprinting via high-resolution mass spectrometry non-target screening, to directly confirm human fecal inputs. We also advocate applying causal inference tools (e.g., Bayesian networks, E-value sensitivity analysis) to better distinguish association from causation, and using spatiotemporal mixed-effects modeling with geostatistical mapping (e.g., regression-kriging) to account for autocorrelation and visualize risk with uncertainty. Finally, we encourage translating microbial concentrations into public health context through quantitative microbial risk assessment (QMRA). These enhancements are feasible and would increase the study's relevance for guiding water safety interventions in Indonesia.