How do I tell an outside leak from a slab leak?
By what the meter does and where the water shows up. Turn everything in the house off and watch the meter: movement that stops when you close the irrigation valve points outside, movement that continues points at the house. A warm spot on the floor points at a hot-water line under the slab instead.
The two problems look identical from inside: damp baseboard, lifting flooring, a musty cabinet. Which one you have decides who you call, so it is worth ten minutes at the meter before anybody opens a wall. A slab leak is a plumber's diagnosis; an irrigation lateral is a landscaper's.
Pressure testing, dye tests and digging on the pool or irrigation side are that trade's work, not ours. What the crew contributes is the indoor half of the picture: a moisture map that shows where water is entering the building and how far it has reached, which narrows the search outside considerably.
What does flood irrigation have to do with water damage?
It puts several inches of water across a whole yard on purpose. Arcadia, Encanto and parts of Tempe and Mesa still irrigate that way, and the yard holds the water in with berms and gates. When a berm washes out or a gate fails, that water goes wherever the ground slopes.
Arcadia is the clearest example. The area was citrus grove from 1919 until the mid-1950s, served by the Arcadia Water Company, and when ranch homes went up on those big lots the irrigation system stayed. Yards there are still flooded on a schedule beneath orange and grapefruit trees, which is charming until a gate sticks.
A short walk before the water arrives is the whole defense. Check the berms and gates, clear anything that would push flow toward the house, and look at the threshold under the garage door. If water has come in before, the fix is grading, a berm repair or a threshold seal, which is landscape work rather than restoration.
Does the crew find the leak?
It finds where water is entering the building and how far it has traveled, which is usually enough to tell you which contractor to call. Pressure testing a pool line, running dye or digging up an irrigation lateral is pool and irrigation work, and this crew does not take it on.
You get the moisture map, the photographs and the dated readings to hand to whoever does come out. That shortens their search and gives you something concrete if the first contractor says the leak must be somebody else's.
There is an insurance angle worth knowing early. Policies commonly exclude long-term seepage and gradual leaks, and a line that has been watering the ground for a month is exactly that kind of claim. Ask your agent what your own policy says, because coverage is decided by your insurer.
Why is soil water treated as contaminated?
Because of everything it passes through on the way. Water that has run through yard soil, a planter or a valve box picks up dirt, fertilizer, animal waste and whatever else is in the ground, so it is handled as gray rather than clean water. Carpet pad and similar porous material it reached usually comes out.
The ground here also moves water in unhelpful ways. Valley soils are described as alluvial with hard caliche layers, and a layer like that can stop water soaking down and send it sideways instead, traveling until it meets the edge of a slab or the footing of a block wall.
That is why the wet spot indoors can be a surprising distance from the broken line. Readings taken over several days separate a one-off soaking from a continuous source, and structural drying only starts in earnest once the source has been closed off.