You don't need to diagnose the problem before calling. Tell the plumber what you can see, where it is and when it started. “Water under the bathroom sink, not sure where it's coming from” is a useful description.
Photos and a little history help the shop prepare. They don't replace a visit or guarantee a price.

Include the room or fixture, when you first noticed the problem and whether it is getting worse or returning after an earlier repair. Say whether water is still flowing or whether you've already shut it off.
If you've had work done, send the invoice or describe it. Distinguish what you've observed from what someone told you might be causing it.
Fictional first message: “Gas water heater in the garage. Water has been pooling around the base since Tuesday. I've attached photos of the heater and label. Can you assess it, and what does the visit cost?”
Stay with what you can safely reach. Don't remove covers, crawl into an unsafe space or delay an urgent call to get better pictures. Ask the plumber to document hidden areas during the visit.
For a water heater, say whether it's gas or electric if you know. A clear label photo is more useful than guessing the model or trying to decode its age yourself.

Tell the shop if the heater is upstairs, in an attic or behind a narrow doorway. Mention a tenant, locked gate or property manager who needs to arrange entry.
For repeated leaks, include the dates and locations. Give the same history to each shop so they aren't making recommendations from different information.
TMWA explains the house side shutoff and cautions against using the valve in the street meter box. Use its official guidance for your supply arrangement. For an active emergency, use the emergency guide.
Before confirming the appointment, ask what it costs and what that includes. Our service call fee guide gives you the questions to settle when booking.
