“Ground Water” vs. “Surface Water”: How To Tell Them Apart, by Daniel Blum

Sometimes you notice an unmistakable musty odor when you walk in the front door of a house. Maybe you’ll see white or black stains on the cinderblock walls of the basement. Or you’ll respond to a call from a desperate homeowner, whom you later find in the basement wearing boots and holding a mop or wet-vac, trying to find a place to put all the storage boxes that used to be piled in the corner. In any case, you need an accurate diagnosis and a cure for a wet basement. 

If a house has a basement, cellar or crawl space below ground, chances are that sometime during the life of the house, water will seep into these areas. If this happens rarely, it can be ignored or treated as an occasional nuisance. When water seeps into a basement frequently, it can cause tremendous cosmetic damage and ruin air quality by promoting mildew growth. In severe cases, persistent water seepage may be associated with structural problems with the foundation or wood framing. Water in a crawlspace underneath a house can do a lot of damage to the structure above it, especially if the space is poorly ventilated. Unfortunately, underground water problems are one of the most misunderstood areas of home maintenance. The purpose of this article is to enable a non-expert to quickly distinguish the likely source of water seeping into a home, and to understand the appropriate remedies.

Virtually all water seepage problems are the result of “soil saturation”. Normally, the underground soil is capable of absorbing water like a sponge. The soil is able to absorb more water until all its voids are filled up. At that point, any added water will build up in height and increase in pressure. This “hydrostatic pressure” then pushes the water through small cracks and pores in a wall surface. This is the mechanism for water seepage in any basement or crawlspace.

Most basement waterproofing companies promote one particular remedy in their sales pitch. The contractor will propose to break open the concrete and dig a trench around the perimeter of the basement floor. Water entering the basement is intercepted by gravel in the trench and carried to a trash-can size “sump crock” under the basement floor. A sump pump is installed in the crock to discharge the accumulating water to a safe location in the yard. New concrete is then added to conceal the trench. The resulting system is sometimes called an interior dewatering system, a perimeter drain, or a french drain.

The problem with this “one size fits all” approach to waterproofing is that it may result in a homeowner paying several thousand dollars more than they need to for unnecessary equipment, or for a solution that does not remedy their specific problem. A dewatering system is most suitable for correcting “ground water” problems, but according to local authorities, the majority of basement water problems in this area are due to “surface water.” To make matters worse, an uninformed homeowner may be persuaded sign a contract charging two or three times the going rate for this type of installation.

Ground water refers to clear water contained in underground lakes or streams, the same water that is tapped for wells. Surface water is rain and melting snow which falls in the yard near a house or which lands on the roof. While the distinction between the two is somewhat artificial, it is very practical to separate water problems into one of these two categories.

What normally happens to roof and yard runoff? When a house is built, the architect is supposed to locate the house higher than the surrounding street and yard. The builder is then supposed to create a combination of gentle hills and valleys which cause water to flow away from the house to the street or to a remote area. This is what is meant by “grading”. When it is done properly, only a small fraction of the little rain and snow will enter the soil next to the house. The ideal grading job will result in a tightly compacted clay-soil surface sloping consistently downhill away from the house for at least six feet in all directions. If roof gutters and downspouts are functioning properly and are extended far enough from the house, the roof water will run off safely as well. This combination of gutters and grading is essential to prevent excess water from soaking the soil around basements and crawl spaces.

Since most houses have gutters and grading, why are water problems so common? Usually, because one or more of these surface water controls has been neglected or disrupted. Builders routinely do not compact their graded soil surfaces tightly enough. Then when landscapers plant shrubs next to a foundation, they reverse the slope of the ground around a house and deliberately loosen the soil, which totally defeats the grading. Gutters and downspouts routinely become clogged with leaves and debris from nearby trees, and downspouts discharge their water too close to the house. In these situations, a large concentration of water enters the soil very close to the foundation, promoting soil saturation.

When poor surface water controls are identified as the cause of a water problem, improving the grading and extending the downspouts will almost always eliminate or greatly reduce the problem. The cost for this type of remedy is usually much less than for a dewatering system, and it can be successfully accomplished by an able-bodied homeowner or yard work assistant.

By contrast, ground water is a semi-permanent flowing reservoir of water contained by rock layers. The top surface of this body of water is called the “water table.” If ground water rises all the way to the surface and spills onto the ground, we call it a spring. When it spills into a basement, we call it flooding. A dewatering system is the only practical remedy for this situation.

So how can you tell whether the water problem you are seeing is the result of surface water or ground water? The following is a diagnostic guide which will allow you to quickly distinguish between the two in most cases.

TIMING: Surface water symptoms appear within minutes or hours after the onset of a rain. When the rain stops, the symptoms also diminish shortly afterward. Ground water problems may occur during a period of totally dry weather and may appear and disappear without any relationship to the daily weather conditions. They may be seasonal.

ONSET AND DURATION: Surface water problems appear suddenly and do their damage during repeated short periods. Ground water tends to build up and recede gradually. It will have long duration or may be continuous.

LOCATION: Surface water symptoms tend to be localized in areas of the basement near concentrations of water on the outside of the house. Ground water will be more widespread than concentrated, and will probably not be associated with particular sources of water outside.

SYMMETRY: Water symptoms appearing in a vaguely triangular arrangement, often in the corners of a basement, are peculiar to surface water. Ground water tends to soak the bases of walls horizontally from the floor up to a certain height and no higher.

NEIGHBORHOOD: Surface water problems are usually associated with one particular house. Ground water problems often affect an area of more than one home. If neighbors surrounding a home are also experiencing serious water problems, or if there are springs nearby, there is more likely to be a ground water problem.

TYPE AND SEVERITY OF SYMPTOMS: Surface water is usually associated with whitish minerals appearing on the inside surface of walls, staining, silt, and sharply localized water damage to walls and baseboards. Ground water is associated with “flood marks,” faint, dried out water lines indicating a prior elevated water level. Flooding to a depth of more than one inch is most often caused by ground water.

COLORATION: Surface water tends to be muddy or to carry a fair amount of silt. Ground water is usually very clear and rarely contains silt.

Big thanks to Daniel Blum! 

Read More:

How To Water Proof Your Basement

Step-by-Step: How to Dry Out Your Basement