To prevent water from leaking through your foundation, look to gutters for your first line of defense. While gutter-and-downspout systems protect your house from rainwater and snowmelt, they can also compound drainage problems by concentrating roof runoff at a house's corners close to the foundation. To carry water away, attach a sloped leader to each gutter and guide water at least 10 feet from the foundation. Alternatively, downspouts can dump directly into an above- or underground catch basin. In that case, runoff should be carried through a solid drainpipe to a drywell, an in-ground perforated tank that collects water and lets it seep into the ground. In the past, drywells were 55-gallon oil drums with holes punched in them. From the start, these were doomed to fail as they rusted and collapsed. Today's high-impact plastic drywells are easy to handle and work efficiently on small drainage problems. Larger pre-cast concrete drywells require machinery for their installation but will handle larger volumes of water.
Houses without gutters often have leakage problems caused by water splashing against the foundation. In this case, a collection system should be installed at the roof's drip line. Dig a v-shaped trench, line it with thick plastic and lay in a perforated pipe, pitched toward a drywell or outlet pipe. Then cover the pipe with landscape to keep out dirt and fill trench with stone to allow water to leech through soil and into the pipe.
Regrading the ground closest to your foundation can also help. Clear away plantings and gently build up the soil to slope away from the foundation. The 10 feet of ground closest to the house should slope at least six inches downward to keep water from seeping into the basement or flooding foundation plantings. However, keep soil at least eight inches away from wood siding to protect against rot and insects.