Water seepage is an important problem to address because prolonged exposure to water can damage your home's foundation and allow dangerous mold to grow. Some cracks or openings may be to small to easily see but large enough to allow water to seep in.
Seeping is especially common in basement walls or walls at least partially underground. Water trapped in the soil around the walls puts pressure on the mortar between blocks and gradually works its way through. If enough water builds up in the cracked mortar, it can begin to seep through the wall. Make sure that your gutters are free of debris and working properly and that your downspouts take water well away from the base of your house.
Poor Window Seals
Seals around windows can wear and eventually create small openings that allow water to flow into your house and down the wall. This is especially common in windows that are close to the ground because the window well can hold excess water against the window seals.
If the air in your home is especially humid, cool surfaces, such as windows or basement walls, could cause condensation that would make it seem as if water must be coming from the outside. Since outdoor temperatures usually drop when it rains, condensation could be more likely to occur on your windows then run down the wall.