There is growing interest in the microbiome inhabiting the built environment and its potential implications to human health (Hanski et al., 2012; Kelley and Gilbert, 2013; Oberauner et al., 2013).

A: You need a hot-water recirculation system. Instead of water moving in only one direction, from the water heater to the bathroom, it also moves cooled water from the bathroom to the water heater, ...