If you notice standing water under the deck after rainstorms, you may need a drainage system to efficiently move this water. You do not want standing water to rest against your foundation or against support posts for the deck, as this could cause significant structural problems over time. Make sure the area has proper grading, too.

Yes, slab leaks are fairly common, especially in older homes and places that are prone to earthquakes which can move home foundations.

It depends on what caused your basement flooding, the extent of the problem, and the risk of the flood continuing. If your flood is coming from a septic system or sewer line, breathing in the sewer gasses can be dangerous, so you should vacate. If the flood occurs from an ongoing natural disaster, relocating to a safe area might be wise. If you just have a plumbing leak or rainwater coming in, you can likely stay in the house if you don’t have electrical lines down there, but make sure you call in professionals to fix the issue immediately.

A sewage smell in your crawl space is usually from a damaged or clogged pipe leaking sewer gasses or actual sewage underneath your home, but there are some other common causes. Moisture, from poor or damaged encapsulation or a malfunctioning sump pump, can harbor mold and bacteria, causing a musty smell. Pests can also get stuck in your crawl space and die, which causes a sewage-like odor.