You know you have a basement problem, but where do you go from there? There are many different companies offering different services. Some are effective, some are not, often because of incorrect assumptions about geology, ground water and soils.

If the processes are not understood, the probability of success of a given treatment is reduced to pure chance. The problem is further confused by the fact that what works in Olney may not work in Mount Vernon or in Cheverly, or may even make the problem worse.

Inside channeling is a common treatment in this region. Holes are drilled through a wall to allow water to enter. A channel drilled in the floor leads to a sump pump, which sends water back outside. The system is completely internal, does not disturb the outside in any way, and initially may appear to be cheaper than backhoe rental, gravel fill and re-landscaping, although the dollar figures should be checked carefully, as should its probability of success. A spectacular example of failure is a local house with a serious water problem that was treated with inside channeling, 11 sump pumps and many thousands of dollars. It didn't work.

The critical question is, "Can water actually reach the drain?" If the material behind the wall is permeable all the way to the footings, the technique can be successful. This condition exists where the wall was backed with a dry well so that water collects in a mass of permeable material, but no outlet was provided. Inside channeling provides that outlet, and although one has essentially let the cat in, it is a viable choice given these conditions.

If the wall is bulging, possibly with a slow seep of water, chances are excellent that the wall is undrained and in contact with a heavy (possibly swelling) clay. In this instance, inside channeling will be a complete waste of money.

Water, pressure or bulging halfway up the wall will not be relieved by tiny drain holes at the footings or by any number of sump pumps, simply because water can't get to them. The problem must be attacked from outside. But replacing the outside drainage system then also makes the inside channeling pointless.

Clay injection as an attempt at waterproofing is no longer used in this region, at least as an advertised service, because some houses here collapsed when the process was used a deacde ago, making their owners very unhappy. It is, however, worth mentioning because variations on the underlying reasoning are still common in construction.

An expanse of clay, such as bentonite or montmorillonite, was injected into the soil in dry form on the theory that it would swell, forming a waterproof barrier to ground water. These materials certainly do swell -- by up to 200 percent -- and are used in ponds and earthen dams for that very reason. But pond bottoms and earthen dams are very different in structure, purpose and behavior from masonry walls. In the process of swelling, montmorillonite can exert pressures of up to 33,000 pounds per square foot. A wall already under stress from water or earth movements does not need more stress.

The first step to successful treatment is to distinguish between surface water and ground water. Surface water is usually clear and comes in a whoosh during or immediately after a rain, while ground water tends to be colored by the soil it has passed through. Many apparently severe water problems are due to downspouts dumping rain directly from the roof into the basement via cracks or door and window wells.

In one extreme example, a Prince George's County man a few years ago carefully tucked the downspouts under the foundation of his home. When he one day noticed water spurting from the holes into which he had tucked the downspouts, he carefully sealed them with concrete. The center of the basement floor subsequently rose by about six inches because of water pressure and water-induced foundation movement.

The good news is that such problems are remedied easily by directing water to a point down and away from the house. The bad news is that if pure surface water, with no serious pressure behind it, is flooding into the house, there is a crack somewhere or inadequate or deteriorated waterproofing compound, called parging, on the outer surface of the wall, which in turn may leave the basement vulnerable to ground water.

What is the best treatment for a wet basement or foundation? Providing proper foundation drainage as should have been done in the first place. The Ideal Basement is constructed as in the diagram on page E1. Successful treatment of most water problems requires the creation of the same conditions, that is, permeable material in contact with the entire cross-section of the wall, with provision for removal of collected water.

When this work is done as a remedial measure after construction, the system is often referred to as a French drain. The term is often applied interchangeably and incorrectly with the term dry well, but both terms and structures are commonly confused and misapplied.

In theory, a dry well is a gravel-filled trench that intercepts and holds water until it can be removed through evaporation. In fact, evaporation in the 98 percent humidity and thunderstorms of the average Washington summer, and underground to boot, cannot possibly keep up with any reasonable supply of water. Water is actually lost from the well by filtering into the soil.

The dry well intercepts not only ground water, but also surface water that might otherwise have run off, so that there may be more water in the area than there was to begin with. Because evaporation is negligible and no outlet is provided, water level may rise. Saturation of surrounding soil may result in reduced bearing capacity or failure of the foundation materials.

A far better solution is the French drain, also a gravel-filled trench, but with an outlet. Ideal design allows water to drain through gravity to a lower area, so the base of the trench must be sloped about 5 degrees to allow water to move easily toward the outlet. If the topography is uncooperative, a sump pump is used.

Please note that the depth of this construction should extend down to the footings, and the outlet is in the bottom. If footings are 6 feet below the surface, any drainage structures must go down 6 feet. The outlet must be deeper and the point to which any water is expected to drain must be lower still.

When dealing with ground-water problems, remember that the basement is not on the ground. It is obviously under it, which is why ground-water problems are not resolved by sloping the ground surface away from the house, as is so often recommended. That takes care of surface water only, which is important, but certainly not the whole picture. Be sure to think in terms of the basement going under the ground.

I recently saw a so-called French drain that was intended to drain a foundation at least 7 feet deep, but the drain was dug only to a depth of 4 feet and the only outlet was a length of plastic pipe sticking out of the top. Water might burble out of the pipe if the "drain" should fill to the top, but that is not what drains should do.

If a builder says that a house is equipped with a dry well or a French drain, or if a contractor proposes to build one, be sure that you know precisely what is meant and why.