Microbial growth comes from moisture nutrient temperature and darkness, keeping moisture away from inside walls, ceilings, and floors prevent any microbial present, also under sinks there are water lines supplies washer hoses, refrigerator water filter lines and cooper burst pipes can burst causing water leak, flood and if not one notice there a lot chance of microbial growth. having your plumber inspect your home plumbing is not bad idea one a year will help prevent this mayor water damage in your home.