How can water get into your home? Let me count the ways. On second thought, let me just try to describe many of the ways. Water is endlessly creative in finding its way into things that we think are tightly sealed.

We have a free ebook available, “How to Find Mold and Moisture Problems in Your Home: Secrets of the Professionals.” If you haven’t already downloaded it and read it, now’s the time to grab it. Go here to get it. Inside, you’ll find a comprehensive guide to inspecting your home and finding signs of water and moisture problems. If you find moisture problems, it may be time to test your air for evidence of indoor mold growth. If someone in your home is chronically ill, or just not feeling well, a mold test is imperative.

Water matters, because without it mold won’t grow. Of course, without any water, no life will grow. But humans, pets and plants can get by on lower relative humidity than mold. Mold is happy in the same temperature range people like. And pretty much everything people use to build homes and furnish them is pure mold candy, as long as there’s enough water.

How much water? Well, 50 percent relative humidity or more is adequate for mold. It helps if the air is fairly still, too. This explains why so many schools have mold problems every fall: They are closed up in June with no ventilation or air conditioning, giving mold a nice summer vacation with warm, humid air to grow and get healthy. Healthy mold means sick people. Often they make it even healthier by shampooing the carpets in August, and leaving the windows closed and the AC off. Yow.

So water can come in with the air. Air conditioning dehumidifies, so homes with AC can keep their humidity levels down during the summer. But AC creates other moisture issues. The condensation created in the AC unit itself needs to drain outside the house. If that drain is clogged or leaking, there’s a source of excess moisture. Dehumidifiers can help too, and one advantage is they don’t lower the air temperature outside the unit.

Temperature differentials are another issue created by AC. Even in the driest of climates (think Arizona), you can have condensation forming in wall cavities and attics, where the cool inner wall or ceiling meets the warming outside air, bringing it down to dew point. This can produce enough moisture to support mold growth that’s completely invisible.

Bathrooms are a great source of water (no, duh?), sometimes in unexpected ways. Obviously, drips and leaks create excess moisture where it doesn’t belong. Exhaust fans vented into attics or crawl spaces are another common water-maker. But how about a bathroom with an open window and no exhaust fan (there are a few million of these)? You can bet on moisture in the ceiling space above, or in the attic/crawl space. Water vapor can penetrate almost anything, and even with a properly vented exhaust fan you can still end up with a moldy attic if the fan isn’t powerful enough or doesn’t run long enough.

Tub and shower surrounds, tile and grout all can leak and deposit moisture in wall and floor cavities, promoting mold growth. Kitchens are another obvious source of excess water, as are windows, doors, roofing, siding, gutters, etc.

Then there is concrete. They make swimming pools out of this stuff, so it ought to keep water out, right? Not so much. Basements are notorious for being damp enough for mold growth, but water can also intrude into any space that’s below grade, such as a ground-level room with a block knee wall below grade – very common in split levels. Water in the soil actually bears against anything that blocks it with tremendous, persistent force, called hydraulic pressure. The slightest porosity will allow more water through than you’d imagine.

A slab foundation, meaning a home with a solid concrete first floor, can wick moisture up out of the ground and feed it into wood framing, carpeting, etc., creating a chronic mold problem. Outside grading is also a major factor in water intrusion. If the soil around a structure slopes toward the structure, it carries water in that direction and creates hydraulic pressure against the foundation. Water will eventually seep in.

So we know that mold is everywhere, and water is everywhere. The trick is to keep them apart, and the only way to do that is to be constantly on the lookout for signs of water intrusion or condensation.

With apologies to Thomas Jefferson, the price of mold freedom is eternal vigilance.

Again, if you haven’t downloaded your free copy of “How to Find Mold and Moisture Problems in Your Home: Secrets of the Professionals.” you can still get it here.

Have dry and mold-free day. And of course, if you feel you need to test for mold, remember that not all home mold test kits are created equal. For a comprehensive comparison of mold detection kits, click here.