Positive grading and drainage are essential to the welfare of a property, and are usually the primary concern of architects and builders. Moisture can deteriorate most surfaces, and the ideal site will be graded to conduct water away fro m a building. In fact, the ideal building will be surrounded by hard surfaces that slope way from the exterior walls, t he interior floors will be several inches higher than the exterior grade, and the building will have gutters and down spouts and a system of drainage designed to prevent any moisture from threatening the foundation or the living space. Unfortunately, many properties do not meet this ideal, conditions on most can generally be improved, and all need to be monitored and maintained to prevent damage. Also, inspectors cannot see inside area drains and do not water-test them, but they can become blocked by debris, occluded by silt, and damaged by movement. Therefore, buyers should question sellers about the functionality of any such system, have it serviced by a specialist, or assume the risk of having a system that does not function well and the damage that might result. A home inspector cannot determine the effectiveness of grading and drainage during excessive rain or unusually heavy rain such as during an el nino event.