Controlling subsurface groundwater
If no surface water sources are found, then the source of the water is likely subsurface groundwater under hydrostatic pressure. Unfortunately, subsurface groundwater problems are more difficult and more expensive to fix than surface groundwater problems.
When the groundwater levels outside the basement rises above the level of the floor, the basement acts like a boat in a pond. If a boat is sitting in water, water will leak in through any open cracks or holes. It works the same way with a basement. Hydrostatic pressure can push water through hairline cracks. Symptoms of this are water coming up through cracks in the basement concrete floor or water coming in at multiple locations.
If you have an older house within town and the house has a basement with no sump pump, it is likely the perimeter foundation drain system connects directly into the city storm sewer system. If the level of the basement is below the street level, there is the potential of storm water backing up in the city storm sewer system and being pushed into the perimeter foundation drain system. This can saturate the soils around the house at the basement level with storm water under hydrostatic pressure, causing water to leak in. Another source of subsurface groundwater is an underground spring.
No matter where it is coming from, the best way to control subsurface groundwater is to install a sub-floor perimeter drain system to relieve hydrostatic pressure. The groundwater is pushed into the drain system and not into areas where it can damage carpets, walls or belongings. The water drains by gravity into a sump pit where a sump pump discharges it out of the house. There are two basic types of drain systems for wet basements. One is a perimeter above-slab gutter system installed at the base of the exterior foundation walls on top of the floor slab. It doubles as a base material for the wall. The other type of drainage system and the most effective, is a below slab perimeter drainage system. The below slab system requires the partial removal of the concrete floor slab and installation of drainage pipe making it more labor intensive than the base gutter system.
It is well known in the industry that an under-floor drainage system is better because the under-floor drains are proven to relieve the hydrostatic pressure before the water reaches the bottom of the floor slab.
Storm water backing up into your home
In many older houses with basements (mostly pre-1980), there is a perimeter foundation drain outside the exterior wall, at the level of the basement floor, next to the footings at the time the house was built. A pipe was usually installed from the perimeter foundation drain to the street where it was connected to the city storm sewer system.
This can become a problem as the city storm sewer system becomes too small when more development causes more rain runoff. When this happens, the rainwater in the sewer system can get so high that water flows backwards toward the house. The perimeter foundation drain fills with water and releases large quantities into the soil next to the footing and basement floor. The soil becomes water-logged and the water which is under hydrostatic pressure leaks into the basement.
Usually the installation of an interior perimeter basement drain system connected to a sump pump will take care of the problem. The interior perimeter basement drain system can usually pump the water out and onto the ground as fast as the water is backing up from the city storm sewer system.
If that doesn't take care of it, the other, more expensive alternative would be to dig up and cap the pipe that is running from the house to the street from the perimeter foundation drain. However, this is not always possible because many times, this pipe is also draining sanitary waste from toilets and sinks in the house.
Sanitary sewer water backing up into your home
If the water is coming up through floor drains or sink drains in the basement, then the problem is likely water backing up from the municipal sanitary sewer system. This usually occurs in older sections of some cities that have combined sanitary and storm sewer systems. During heavy rains, combined sewer systems can become overwhelmed with water. This can cause sewer water to back up in the system and sometimes into homes.
You can imagine the mess this creates for homeowners because it usually means they are getting other people's fecal waste backing up into their basement. To correct this, cities should update their sewer systems so the sanitary sewer and storm sewer are running in separate pipes. Until this work is complete, the homeowner can install backflow preventers that help stop sewer water from flowing backward into the house.
Unfortunately, because the city sanitary system works in conjunction with every house sanitary piping, the backflow preventer usually cannot be located on the house's main sewer line. It usually requires several backflow preventers at all basement drain locations, such at every floor drain, sink and toilet. These backflow preventers require routine maintenance to make sure they are kept free of debris.