Plumbing in California is a mix of eras and soils, and the leak usually follows both. Older city houses still hide galvanized supply lines that have narrowed to a trickle and started to pit. Many southern and valley ranches sit on slabs, where a hot-water line can seep under the floor for a long time before the bill or a warm spot in the tile gives it away. Clay yards in the central valley and in older neighborhoods invite tree roots into sewer laterals. Hillside laterals in coastal cities can run a long way from the house to the main, and they fail in the yard rather than under a sink.
Fixtures are the last chapter, not the first. A dripping tub valve, a toilet that rocks, a water heater that rusts at the base, or a kitchen drain that burps are symptoms. Behind them you may find mixed metals, a tired angle stop, a vent that does not vent, or a cleanout buried in a planter. Garages hold a lot of water heaters in the south. Tight closets hold them in city flats. Either way, a failed pan or a missing drain turns a heater leak into a floor problem.
Climate changes the urgency. A slow seep in a dry inland summer can travel under a slab without a stain until the damage is wide. A winter rain in the valley or the bay can fill a broken lateral and send water up a floor drain while you are blaming the shower. Hard water leaves scale in heaters and valves in much of the state. Soft coastal air does not save old steel pipe. If you only replace the fixture that looks bad, you can leave the line that caused it untouched.
Call with the symptom and the age of the house in plain words. Say whether water is showing up on a ceiling, a slab, or a yard. Say whether drains are slow in one fixture or in every fixture on that side of the house. Mention the water heater location, any shutoff you already turned, and whether trees sit over the sewer route. Supply, drain, and heater work are different calls, and the description is what sorts them.
Call the number on this page.