When you picture a plumbing leak, you probably picture a leaky faucet or perhaps a drip from an exposed pipe like one under your bathroom sink. However, the most serious plumbing leaks in your home are the ones that aren’t visible—at least not if you don’t know what to look for. Plumbing leaks can be insidious, building up for a while before the damage becomes severe enough to draw attention. A leak can be hiding anywhere in your home, including behind your walls, under your floors, or above your ceilings.

These five warning signs can help you identify a small leak before it becomes a big problem:

1. Sounds of running water

In a home with multiple floors and occupants, it’s common for water to be running for one reason or another—someone’s doing laundry, taking a shower, or running the dishwasher. Running water is so commonplace we learn to tune it out completely. However, if you start to notice the sound of running water when no one else is home or you know that nobody is using any faucets or showers, it could be a sign that you have a leak somewhere.

2. Unusually high water bills

Month to month, our water bills usually fall within a predictable range, within a $10-15 fluctuation. If you start to notice that your bills are climbing without any corresponding change in your water usage habits, there may be a leak that’s draining excess water. High water bills are the most accurate sign of a leak somewhere in your pipe system.

3. Musty Smells

Anywhere there is moisture collection your home can quickly become a breeding ground for mold and mildew. Even if there aren’t any visible signs of moisture, eventually these spots will begin to produce the telltale musty odors of fungus growth. If you start to notice this smell, call your plumber to help you track down the source of the moisture.

4. Damp spots

Any discoloration or dampness on your floors, walls, or ceiling that can’t be traced to a spill is probably a sign of a leaking or damaged pipe. If you notice a damp spot, don’t ignore it and think the problem will go away on its own. The more moisture you allow to build up, the more likely that serious damage will result from toxic mold growth or a burst pipe.

5. Foundation cracks

A long-term leak or crack in your pipes can eventually start to cause cracks to form in the foundation of your home. We don’t need to tell you that this is a serious problem. Cracks naturally form over time as a house settles into its foundation, but if you’re noticing a rapid multiplication, you probably have a leak. This should be dealt with as soon as possible—long-term leakage will weaken the structural foundation of your home, potentially even causing your walls to start cracking.

Be on the lookout for these common warning signs of plumbing leaks. If you become aware of any of these signs in your home, contact Bonfe right away to solve the problem before it can cause serious—and costly—damage.