SUMMARY In communities with high rates of diarrhea and enteric infections, the spatial scale of bacterial strain sharing in young children has not been well studied. Yet, understanding these transmission patterns is critical knowledge for selecting and implementing interventions to protect child health in resource-constrained environments. Water treatment interventions are often targeted at the household level, yet recent large-scale trials of household-level interventions have not consistently shown reductions in child diarrhea prevalence. One explanation is that household-level drinking water interventions fail to disrupt community transmission pathways, resulting in continued child exposure to bacterial pathogens. Here, we will investigate strain sharing between child pairs at multiple spatial scales, including within households and between households across urban and rural settings. We will leverage previously collected (by our team) fecal samples from 240 sets of siblings (n=480 children), including siblings from 120 urban households and 120 rural households. In both urban and rural study sites, we will have the unique opportunity to sample from equal numbers of households from villages with and without access to community-wide drinking water chlorination. We will 1) compare the scale of bacterial strain sharing in rural versus urban communities in Kenya; and 2) evaluate the effect of access to community-wide chlorination on bacterial strain sharing in both urban and rural communities. Our study population will also allow us to investigate if bacterial strain sharing patterns and community-wide water treatment effects differ for younger versus older school-aged children. We will use short-read metagenomic sequencing and a new innovative suite of computational bacterial strain tracking tools developed by our team to achieve these aims. Our findings will inform the scope and scale at which future drinking water and other environmental interventions should be implemented, and if the delivery of interventions designed to protect young children from exposure to bacterial pathogens should be different for rural versus urban communities.