Matching symptoms to the correct service
If only the hot water runs cold while cold taps still flow, the issue centers on the water heater itself rather than the main supply. Whole-house low pressure that improves after the meter points to the service line or a partially closed curb stop. Slow drains isolated to one fixture usually stay within that branch until the trap or vent stack.
When sewage odors appear near the cleanout or multiple fixtures back up together the restriction sits in the sewer main or house trap where roots commonly invade. Gas smells require immediate valve shutoff at the appliance and meter before any further testing. Matching the pattern of symptoms to these common locations prevents unnecessary work on unrelated sections of the system.