Groundwater & Basement Water Intrusion in Gilbert, AZ

It is, because almost none of what falls soaks in. Caliche beneath thin desert soil absorbs very little, so a monsoon cell dropping an inch in under an hour produces runoff at close to the full rainfall rate. Streets and washes carry it and it reaches buildings within minutes. The annual figure describes how little rain arrives; it says nothing about what happens to the rain that does.

It can, in ways that are easy to miss. Much of this area was leveled and flood irrigated for decades, which left engineered grades, ditches, and sometimes buried structures beneath what are now subdivisions. Those features can still route water, and they were designed to spread it across fields rather than to move it away from houses. Where a lot floods for no apparent reason, the historical land use is worth investigating.

Plumbing and appliance failures, by a considerable margin, rather than weather. In a climate this dry, most of the water that damages houses arrives from a supply line, a water heater, or a refrigerator connection. Slab construction means those failures often surface late, after the water has traveled under the floor. The most useful precaution is knowing where the main shutoff is and how quickly it can be reached.