In homes built on a slab, the main supply valve will either be in a first floor utility room or, possibly, a garage in warmer climates. If the house is on a municipal water supply, the valve will usually be on the foundation wall facing the street. Water supply lines exist in a closed loop, save for the shut-offs to individual fixtures like sinks and toilets. Similarly, if you have battery-powered smoke detectors, I would advise replacing each of them with new 10-year battery detectors. Ecoey 10-Year Carbon Monoxide Detectors, 4 Pack $65 at Amazon5.