Basements most commonly leak water through the joint where the floor and wall meet and through mortar joints. This is typically after rain or when snow has begun to melt. However water can come up through cracks in the floor as well. Surface water works its way to the foundation. As footer drains start to clog or drain more slowly over the years, water builds up around the foundation, and creates hydrostatic pressure around the walls and under the floor. Water is forced through the joint where the floor and wall meet and through the foundation wall its self. Clay absorbs the water under pressure and swells causing walls to crack and bow, also the same cracking happens under the basement floor.