At One Call Plumbing, the plumbing business where Mr. Calazans works, employees have been answering the phones nonstop in a small office with sprawling maps of Houston on the walls. The owner, Edgar Connery, said he had been in the business for nearly 40 years and had never seen a crush like this after other natural disasters. Some other companies had gotten so swamped that they stopped answering the phone at all.

Mr. Calazans returned to work in the field on Thursday, going from one customer’s house to another, mainly to size up the damage. Simple problems he repairs on the spot if he can. But some houses will need major work, and may even have to be re-piped completely; those must be left for the weeks ahead.

Obtaining the materials to get even the simple jobs done is a growing problem, Mr. Calazans said: Waiting in line at a supply house could tie him up for hours, but when he tried picking up a few things at Home Depot, the shelves were bare.

“I’m literally just burning through supplies,” he said.