In order to know how to waterproof a basement, you need to know how water enters the basement. There are many different ways water can enter the basement: floor / wall joint, floor or wall crack, or through the bulkhead, to name a few.
Here we are going to talk about how water enters through the floor/wall joint.
The floor/wall joint is the most common entry source of water entering the basement. This is where the foundation wall meets the floor. The water comes in from the outside over the footing under the foundation wall and through where the foundation wall and floor converge. This is seen mostly when it rains. Water may seep in from other locations, but the most heavy water intrusion will be from the floor/wall joint.
When one concrete structure is poured (the floor) and another concrete structure is poured on it or next to it (the wall), a seam is created between the two concrete structures. Each concrete structure (the footing, the wall and the floor) is poured separately. There is a seam between each of these three structures. This allows the potential for water to come into the basement. There are four potential points of entry now: over the foundation footing, between the foundation walls, underneath the foundation and up through the seams between the foundation footing and the floor. This floor/wall joint seepage is very common and is a predominant reason for basement flooding.