A leak isn't a mold problem yet. The 48 hours after the leak are what decide whether it becomes one. Mold needs three things to grow: a food source (your drywall, wood, insulation), oxygen (always present), and moisture - the only one you control.
Here's the checklist for the first 48 hours after you discover a leak, in order.
Hour 0-1: Stop the water
Shut off the supply at the source. Under-sink valve, toilet shutoff, or the main if you can't isolate it. Don't try to clean up while water is still flowing. Take photos of everything before you move anything. Your insurance adjuster will want them.
Hour 1-4: Move what's wet off what's not
Lift soaked rugs off the floor. Move furniture out of the room. Pull books and boxes off the floor in the basement. The longer wet items sit on dry items, the more material becomes contaminated.
Hour 4-24: Air movement, not just towels
Open windows on opposite sides of the affected area for cross-ventilation. Run box fans pointed across the wet surfaces (not at them - you want airflow, not impact). If you have a dehumidifier, run it on the lowest humidity setting and empty the tank every few hours. Pull baseboard if you suspect water got behind it. Cut a small inspection hole in drywall (above the floor, where the water line ends) and feel inside the cavity.
Hour 24-48: Decide whether it's drying
Buy or borrow a pin-style moisture meter ($30 at any hardware store). Check the affected drywall, framing, and subfloor every 6 hours. If readings are going down, you're winning. If readings are flat or rising at 24 hours, you need professional drying equipment - air movers, desiccant dehumidification, sometimes heat injection. Standard household fans aren't enough for anything past surface water.
What insurance does (and doesn't) cover
Most homeowners' policies cover sudden and accidental water damage. They do not cover damage from slow, long-term leaks ("maintenance issues"). If you discover the leak the day it happened and document it, you're usually fine. If you discover it three months in, the claim gets harder.
When to reach out
Reach out within 24 hours if (1) the leak ran for more than a few hours before you noticed, (2) water reached insulation or a wall cavity, (3) it's category 2 or 3 water (dishwasher drain, washing-machine drain, sewer, or any unsanitary source), or (4) moisture readings aren't dropping after 24 hours of active drying.
We can usually be on site the same day. The earlier we're involved, the less we have to remove.