Microorganisms are ubiquitous in our homes. Although most of these microbes are innocuous, some of these household bacteria and fungi can have important impacts on human health. Unfortunately, we have a limited understanding of how these household microbial communities vary across different geographic regions or the factors that structure their biogeographical patterns. I will highlight two recent projects that leverage the power of ‘citizen science’ to investigate the microbes found inside homes. In the first set of studies, we collected dust samples from ~1,500 households across the U.S. to understand the continental-scale distributions of airborne bacteria and fungi inside homes. We assessed the diversity and sources of these airborne bacteria and fungi, yielding our first insight into how airborne microbial communities are influenced by climate, home occupants, and home design. More recently, we have been focusing on those bacteria living inside showerheads. Showerheads can harbor large populations of mycobacteria, a diverse group of bacteria that includes opportunistic pathogens capable of causing nontuberculous mycobacterial (NTM) lung infections, an increasing threat to public health. To determine how the diversity and abundances of mycobacteria vary spatially and in response to changes in household water chemistry, we recruited >600 volunteer households from across the United States and Europe to sample their showerhead biofilms. We found that showerhead mycobacterial communities vary in composition depending on geographic location, water chemistry, and water source, with households receiving water treated with chlorine disinfectants having particularly high abundances of certain mycobacteria. Regions where NTM lung infections are most common were the same regions where pathogenic mycobacteria were most prevalent in showerheads, highlighting the important role of showerheads in the transmission of NTM infections. Together these results demonstrate the power of a ‘citizen science’-based approach to improve our understanding of those microbes living with us in our homes and their impacts on human health.