Mold is a serious problem following this week's massive storm across the Valley that flooded out several Mesa neighborhoods.
But it's not exactly easy to see.
"Looking at the floors - you can tell what is ruined there," said flood victim Sarah Michal. "But to know how much, and what's up the wall, it's harder to tell ."
Michal and other flood victims are finding out that just because there's no more water in their living room, there still may be a potential problem they can't see.
Mike Lauby with Sunland Environmental Testing spent the day helping homeowners identify moisture in their walls, floors and ceilings.
His thermal imaging camera can help identify moisture that you can't see - moisture that can quickly turn into mold.
"I've seen so much recently where there's no variation in the drywall, no sagging paint, but there's moisture there that you can't see," said Lauby. "That's what can get you if you don't know that it's there."
Lauby spotted a leak in a roof Friday that a homeowner didn't know was there.
The more moisture there is in walls and ceilings, the greater risk of mold growth, said Lauby.
Mold can be an extreme health hazard, especially to folks with asthma, bronchitis and other medical conditions.
Lauby told CBS 5 News that just because a thermal imaging camera spots moisture in a wall, doesn't mean you have to tear it down.
The key is to identify it and dry it out as fast as possible.