Even if you only visit your basement infrequently, you can easily tell when you have issues with moisture. Damp spots might be spreading along the floor, or beads of water will be sweating out of the walls.

This moisture can be particularly concerning if the basement is closely connected to the rest of the home through ductwork or if you plan to finish the space. John Carmody and Brent Anderson, writing for the University of Minnesota Extension, says the water can lead to the formation of mold or mildew, which can be harmful to your health.

If you finish your basement without first taking steps to dry it out, the floor and wall coverings will eventually start to molder and rot. To avoid this problem and keep your basement from getting too damp, you'll need to find out how moisture is getting into your home and work to keep it at bay.

Causes

Moisture in the basement might be the result of condensation or water leaking into your home. The water could be coming from rainfall, snowmelt, a rising water table, or an interior water leak. During the summer, moisture might stem from the condensation of humid air on cool surfaces in the basement.

There is a simple test to see where the moisture is originating. The magazine Family Handyman says you can tape a square of aluminum foil to the basement wall, then check on it a few days later. If the moisture is on the outside surface of the foil, it is a result of condensation. If moisture is present behind the foil, it is a result of water leaking through the walls.

In some cases, it will be more obvious that the water is a result of a leak. It might only appear after a strong rainstorm, or after someone has taken a shower. The Environmental Protection Agency's Energy Star program says condensation affects a wide area, while leaks are usually localized.

Condensation typically occurs if the basement windows are left open on hot days. Warm, humid air will enter through these windows and condense on the cooler wall and floor surfaces in the basement.

Both water and moist air can also enter through cracks or holes in the foundation. Moisture can be pulled through these openings by capillary action or vapor diffusion.

Preventing condensation

The easiest way to cut down on condensation in the basement is to remove sources of humidity. The home improvement site HomeAdvisor says you can consider moving an indoor clothesline outside, especially when hot days are more common.

The vents of clothes dryers can also release a great deal of humid air into the basement. Some models allow you to choose between venting air inside or outside, so make sure you have chosen the latter option. Family Handyman says you can also use foil tape to seal the joints of the dryer vents, where moist air is most likely to leak out.

Make sure your HVAC system is properly sized for your home. The Energy Star program notes that the system will not be as efficient at removing humidity if it is too large for your home or does not create the proper airflow.

If your basement has a dirt floor, water vapor may be coming in through the ground. Covering the floor with plastic will create a barrier between this moisture and the rest of the basement.

Kitchens and bathrooms are common sources of interior moisture, and these areas should have exhaust fans. Run these fans when showering or cooking, and make sure they are not blocked, disconnected, or otherwise functioning improperly. If you don't have ventilation in these areas, consider getting the fans installed.

Keep the basement windows closed during the summer to keep humid air out. HomeAdvisor says you can also improve air circulation by removing unneeded items and creating passageways for air to move. Running a fan in the basement can also help with air circulation.

Installing insulation on the basement walls will keep condensation from developing there. Family Handyman warns that you shouldn't take this step if water is seeping through the foundation, as it can lead to the formation of mold and mildew on the back side of the insulation.

In addition to the walls and floors, condensation can appear on cool pipes and drip onto the floor. Adding foam insulation to the pipes will keep condensation from forming.

While it will not stop the formation of condensation, a dehumidifier can help remove moist air from the basement. Run this device in the basement on particularly humid days.

Plugging leaks

Water leaks may be caused by improper drainage around the foundation. The soil near the side of the home can settle over time, creating a depression where water will run toward the basement instead of away from it. Carmody and Anderson recommend putting down new soil to reestablish a slope leading away from the foundation, with a drop of one inch every six feet.

Restoring this slope could bring soil too close to the siding, increasing the risk of problems such as rot or termites. Jeanne Huber, writing for the National Association of Realtors' home improvement site HouseLogic, says creating a berm or swale—a shallow ditch—will help direct runoff while protecting your siding.

Gutters and downspouts can send water away from your foundation, but only if they are properly installed. Add extensions to the downspouts to make sure water is deposited at least five feet away from your home during a rainstorm. You could also have an underground drain pipe installed for this purpose.

Check the condition of any existing drains outside the home. Clogs can sometimes be flushed out with spray from a garden hose, but you might have to call in a professional to do the job.

Window wells may have developed a slope over the years, or they may have been improperly installed. When this condition occurs, water from rainfall and melting snow will run toward the foundation. Carmody and Anderson say filling the well with aggregate material and creating a supplemental drain will remedy the issue.

If water is seeping in through the foundation, you can try to fill in any openings in this area. Family Handyman says hydraulic cement can be used to patch cracks and holes, while a waterproofing material will fill smaller pores.

For more persistent water issues, install a sump pump system. This pump will collect water at the low point in the basement and pump it outside. While effective, this system can also cost thousands of dollars.

If water damage is visible on the ceiling, the problem is likely a result of a plumbing leak. The Energy Star program says you can hire a plumber to fix this problem, and that you might also have to hire a contractor to remediate any mold issues.