Short of a natural disaster of large proportions, a slab leak is one of the worst problems a homeowner faces. Taking its name from its concrete foundation, a slab is the most important part of your house, the part on which everything else rests, literally and otherwise.

The real challenge in having a slab leak is recognizing that you have one. An undetected leak can cause damage to not only the foundation, but the flooring, drywall and furniture, as well as contributing to humidity and possible mold damage. Here are five signs that you may have a slab leak:

1. Pooling Water

Keep an eye out for water pooling in places it shouldn’t. As water accumulates beneath the slab, it can be forced up and out at the seam of the house and foundation. It may also push up through drains in the kitchen and bathroom. If you notice water in these areas, rule out leaks to appliances and plumbing first. Keep an eye on your flooring too. Wet carpeting or warped hardwood are also signs of leaks.

2. Hot Water Heater Runs Continuously

If your hot water heater seems to be running constantly, it could be trying to keep up with water escaping elsewhere. If that’s the case, you will see a spike in your utility bills as well.

3. Low Water Pressure

A leak means you aren’t getting the full force of water to your faucets. You may notice a weaker stream of water, and also that it takes longer to fill a glass or rinse the soap out of your hair in the shower.

4. Hot Spots on Flooring

If a leak occurs in the hot water pipe, it will heat the concrete and floor directly above it. If you have tile, linoleum or wood flooring, you will be able to tell easily; it’s not likely you will find it through carpeting, however.

5. Mold or Mildew

Water leaking up through the foundation can soak into carpet and drywall, where mold can begin growing in just a few short days. Once it takes hold, you will notice a musty, mildew smell that calls for a close check of carpeting and drywall.

The water and sewer pipes beneath your home’s foundation are susceptible to leaks, just like the pipes throughout the house. Fixing the leak is not easy and requires tearing up the foundation where needed. Finding the leak is tough to do through a concrete slab, and may require your plumber to use special equipment. If you’re looking for a leak, however, you’ve already made it through the hardest part—discovering that you have one.