Most plumbing emergencies don't get worse because of bad luck; they get worse because nobody knew where the shutoff valve was. By the time help arrives, the difference between a contained leak and a flooded floor often comes down to what happened in the first five minutes, not the hour after.
Every home has a main water shutoff, typically where the supply line enters the house: a basement, crawl space access panel, utility closet, or sometimes outside near the foundation. There's also a curb stop near the street that the utility controls, which matters if the indoor valve itself ever fails. Locate both now, confirm the indoor valve actually turns (older gate valves can seize from disuse), and if you manage a rental, post clear instructions with a photo near the valve itself, because a renter at 11pm on a holiday weekend won't know to look in the crawl space.
A burst or actively spraying pipe, a water heater leaking from the tank itself, a sewage backup coming up through a drain or toilet, and a complete loss of heat during a hard freeze are all situations that justify an after-hours call. So is the smell of gas near a water heater, furnace, or boiler; that one isn't a plumbing call at all. Leave the house immediately, do not flip any light switches, and call the gas utility's emergency line and the fire department from outside.
A slow drip, a running toilet, a drain that's slow but not backed up, or a minor leak you've already contained with a bucket can typically wait for a normal appointment. Forcing an emergency dispatch for something that isn't actively causing damage just means a longer wait for someone who has a genuine burst pipe.
Running a garbage disposal or a washing machine to "flush things through" during a backup almost always pushes more water into a space that's already overwhelmed. Likewise, pouring chemical drain cleaner into a fully backed-up line does very little and can make the eventual repair more hazardous for whoever has to clear it.
The houses that flood badly are rarely the ones with the worst pipes. They're the ones where nobody knew which valve to turn before calling for help.
Nece's Plumbing & Heating offers emergency service for the situations above. When you call, knowing roughly what's happening and whether you've already shut off the water helps us get the right truck and the right parts there faster.