Little is known about the biology of microbial populations living in our drinking water. Current systems monitor drinking water for the absence of fecal bacteria using coliform counts, a very old method, and for total bacterial load, which is determined by growing cultures of bacteria found in water samples. Yet 99.99% of bacteria cannot be successfully grown in culture, and thus are missed by using such methods. Our drinking water, in other words, is monitored using very old and inaccurate techniques. This three year grant will fund a project led by Professor Norman Pace at the University of Colorado, Boulder, to use state-of-the art gene sequencing techniques to begin to characterize the microbial populations in municipal water delivery systems. Preliminary work by Pace and his research team on the municipal water supply in Boulder, Colorado has revealed a diverse and (perhaps) stable microbial profile in the Boulder municipal water system, one that differs significantly from the microbial populations in water supplies in New York, New Orleans, and Austin. Funds from this grant will allow Pace to continue and expand this work, as well as provide support for a smaller project to measure how concrete degradation, a common problem in aging municipal water deliver infrastructure, affects microbial populations in the water supply, and funds to complete Pace's ongoing work examining how the flooding of an engineering building on the University of Colorado, Boulder campus changed the characteristics of microbial communities inside the building.