Leonardo DiCaprio and Kate Winslet in James Cameron's 'Titanic.'

A home might have any number of scary structural problems, from mold to a cracked foundation to decaying beams. But what really gets home inspectors’ blood boiling?

“The three things that are going to damage your house most are water, water, andwater,” says Larry Stamp, owner of Cameo Home Inspection Services inOlympia, WA.

After all, most of those “scary structural problems” stem from water. Mold? Give it up for water. Cracked foundation? There are many causes, but a main one is water. And decaying beams? Almost certainly water.

If you’re concerned about moisture-driven maladies, we recommend calling in a licensed home inspector. But if you’re not sure if water’s worth worrying about, here are some ways to see if your home’s at risk.

1. Wobble the toilet

Does your toilet slide from side to side? We’re not talking about just a wiggly base. What you’re looking for is actual movement along the floor, even if it’s just a few millimeters or so. That’s a very dangerous few millimeters. According to Jay Marlette, a home inspector in Berkeley, CA, that could indicate a “common, slow leak around the base of the toilet that’s damaging your subfloor.”

2. Examine the bathroom tiling

Check the tiles around the shower: Is there missing grout, indicated by thin, black lines? Water can easily seep into the bathroom walls and subfloors through those tiny cracks, Marlette says. Give the tiles a hard tap. The resulting sound should be high-pitched; if not, either the tiling was never properly bonded or the glue has loosened. Either way, it’s a sure sign of a current or impending leak.

3. Don’t let dirt and wood touch

Stamp, an instructor at Washington State University, teaches his students that wood and dirt (or bark and gravel) should never touch. Builders should always ensure at least 4 inches of separation between the two, if not more. Soil gets wet and stays wet; wood can’t stay wet, or else it begins to rot.

4. Evaluate your foliage

When you surround your home with too much shrubbery or trees, you might be putting your home at risk of water intrusion. If you’re considering a yard renovation, make sure to engage a qualified landscaper. If you’ve purchased a home with significant foliage, make sure you have an inspector check for adequate clearance between plants and your home—otherwise, Stamp says, it can lead to high moisture and rot damage.

5. Look at the space between doors and the floor

How much clearance is there? If your doors cut too close to the carpet, heating a closed room can turn the air moist.

Water vapor can “rot the walls from the inside out,” Stamp says. “It’s a big deal. It’s a big, huge deal.”

Plan to leave about a half-inch of clearance, depending on the bulk and height of your carpet.

6. Shine a flashlight on the ceiling

Chances are good you can see the obvious brown-colored bubbles that indicate a leaky ceiling with your bare eyes. But if you’re in a newly purchased and recently painted home—or one you’re considering buying—they might not be as visible.

Marlette recommends shining a flashlight obliquely on the ceiling and looking for distorted shadows, “kind of like a welt.”

If your home doesn’t pass the water test, don’t panic: Addressing the problem immediately reduces the chance of it causing major structural damage down the line. After water, nothing irritates an inspector more than complacency.

“I inspected houses 10 years ago that are on the market again now,” Marlette says. “They didn’t do squat.”