The results of The Times’s testing were troubling. Water flowing down Briarhills Parkway in the Houston Energy Corridor contained Escherichia coli, a measure of fecal contamination, at a level more than four times that considered safe.

In the Clayton Homes public housing development downtown, along the Buffalo Bayou, scientists found what they considered astonishingly high levels of E. coli in standing water in one family’s living room — levels 135 times those considered safe — as well as elevated levels of lead, arsenic and other heavy metals in sediment from the floodwaters in the kitchen.

“There’s pretty clearly sewage contamination, and it’s more concentrated inside the home than outside the home,” said Lauren Stadler, an assistant professor of civil and environmental engineering at Rice University who participated in The Times’s research.