Some plumbing problems wait until Monday and some do not. A whole-house backup, a burst supply line, a water heater discharging onto a floor and a gas smell all belong in the second category.
The first thing on any emergency call is stopping the water. We will talk you to your main shutoff on the phone while the crew is dispatched, because the ten minutes before anyone arrives are the ones that decide how much damage there is.
We would rather tell you on the phone that something can safely wait until morning than charge you an after-hours rate for a dripping faucet.
Technician insight
Locate your main shutoff before you need it and check that it turns. A valve untouched for twenty years often will not move when it matters.