Not only does a wet basement feel and smell nasty, it poses a great risk to your home’s value. Left unchecked, basement moisture can ruin floors and walls, encourage mold, even damage roofing.

Some wet basements are easy to cure simply by clearing gutters and by diverting gutter water away from the foundation. But if the problem comes from other sources — water flowing toward the house on the surface, seeping in from underground, or backing up through municipal storm drains — you must take more-aggressive action.

Here are eight strategies to keep water out of your basement.

1. Add Gutter Extensions

If downspouts are dumping water less than five feet away from your house, you can guide water farther out by adding plastic or metal gutter extensions.

But extensions aren’t the neatest or most effective long-term solution, especially if you’re likely to trip over them or run over them with a lawn mower. Permanent, underground drain pipe is invisible and capable of moving large quantities of gutter runoff much farther from your house.

Regrading around a foundation for drainage issues costs $835 to $3,000.

2. Plug Gaps

If you see water dribbling into the basement through cracks or gaps around plumbing pipes, you can plug the openings yourself with hydraulic cement or polyurethane caulk for about $10.

Plugs work when the problem is simply a hole that water oozes through, either from surface runoff or from wet soil. But if the water is coming up through the floor or at the joint where floor and walls meet, the problem is groundwater, and plugs won’t do the trick.

3. Restore the Crown

If the gutters are working and you’ve plugged obvious holes, but water still dribbles into your basement or crawl space from high on foundation walls, that means surface water isn’t draining away from the house as it should.

Your house should sit on a “crown” of soil that slopes at least six inches over the first 10 feet in all directions.

Over time, the soil around the foundation settles. You can build it back with a shovel and dirt. One cubic yard of a water-shedding clay-loam mix from a landscape supply house costs around $30 (plus delivery) and is enough for a two-foot-wide, three-inch-deep layer along 57 feet of foundation.

4. Reshape the Landscape

Since your home’s siding slightly overlaps its foundation, building up the crown could bring soil — and rot and termites — too close to siding for comfort: Six inches is the minimum safe distance. In that case, create a berm (a mound of dirt) or a swale (a wide, shallow ditch), landscape features that redirect water long before it reaches your house.

In small areas, berms are easy; a landscape contractor can build one for a few hundred dollars. On bigger projects, berms make less sense because you’ll have to truck in too much soil. In that case, dig a swale ($450 to $2,000). Once landscaping grows in, berms and swales can be attractive features in your yard.

5. Repair Footing Drains

If water is leaking into your basement low on the walls or at the seams where walls meet the floor, your problem is hydrostatic pressure pushing water up from the ground.

First, check whether you have footing drains, underground pipes installed when the house was built to carry water away from the foundation. (Look for a manhole or drain in the basement floor or a cleanout pipe capped a few inches above the floor.)

If the drains are clogged, open the cleanout and flush the pipes with a garden hose. If that doesn’t work, a plumber with an augur can do the job for about $600.

6. Install a Curtain Drain

If you don’t have working footing drains, install a curtain drain to divert water that’s traveling underground toward your house.

A type of French drain, a curtain drain is a shallow trench — two feet deep and 1.5 feet across — filled with gravel and perforated piping that intercepts water uphill of your house and carries it down the slope a safe distance away.

If the drain passes through an area with trees or shrubs, consider switching to solid pipe to reduce the risk of roots growing into the piping and clogging it. Cost: $10 to $16 per linear foot.

7. Pump the Water

If you can’t keep subsurface water out, you’ll have to channel it from the inside.

To create an interior drain system, saw a channel around the perimeter of the floor, chip out the concrete, and lay perforated pipe in the hole. The pipe drains to a collection tank at the basement’s low spot, where a sump pump shoots it out of the house.

Costing about $5,500, an interior system is the best and least disruptive option in an unfinished basement with easy access. It’s also a good choice if your yard is filled with mature landscaping that would be destroyed by digging an exterior drainage system.

8. Waterproof the Walls

Installing an interior drainage system gets the water out but doesn’t waterproof the walls. For that, you need an exterior system: a French drain to relieve hydrostatic pressure and exterior waterproofing to protect the foundation.

It’s a big job that requires excavating around the house, but it may be the best solution if you have a foundation with numerous gaps. It also keeps the mess and water outside, which may be the best choice if you don’t want to tear up a finished basement.

The downside, besides a price tag that can reach $18,000, is that your yard takes a beating, and you may need to remove decks or walkways.