Poor lot grading can actually be a cause of basement flooding. The function of lot grading is to direct rain water away from your house. When a house is built, the earth around the outside of the house is graded to slope away from the foundation walls. Over time, the direction of this slope can change due to the ground settling and shifting causing the ground to slope towards the house. The result is surface water travels towards the house, down the outside of the foundation wall and into the weeping tiles surrounding your home. You don't want this to happen, you want to keep water away from your house.
Grade your lot so the ground slopes away from the foundation. In addition, extend your downspouts 1.8 metres (six feet) away from the foundation. Always avoid negatively impacting neighbouring properties. Do not push flows to neighbours property or block a flow route through your property.
You should check your lot grading once a year, preferably in the spring, to make sure the earth around the outside of the house hasn't settled causing the ground to be sloped towards your home.
courtesy of City of London