What is a Sump, a Pump and a Sump Pump?

What are a sump, a pump, and a sump pump and can they solve water and moisture problems in the basement or elsewhere on the property.

The term sump references a low collection point for a liquid. This can be used in the automotive field as an oil sump or with other types of lubricants. In the case of this discussion, a sump is referenced as a low point for the accumulation of water.

As we all understand, water flows downhill, which is why drains are pitched in a positive direction. What this means is that the drain line, normally PVC, steel or cast iron pipe is sloped in a manner that establishes the discharge end of the pipe, at a lower elevation than, the intake of the pipe.


A sump is the lowest point in a drainage system that is intended to accumulate water. There are several types of sumps for water or other liquids.

  • Any low point established on the exterior of a structure to accumulate water can be called the sump. These can be identified as an open body of water such as a pond or lake, a low graded area that you may witness alongside highways to accumulate rain water, or even what is referred to as a “ dry well “, which is an excavation filled with a porous media such as sand, rock or gravel that is designed to store water.
  • Engineered tanks and vessels that are specifically intended to accumulate sewage, industrial waste or any other type of liquid accumulation are also called sumps.
  • Sumps established at the low end of a drainage system, around a structure, at the backside of a retaining wall, or any other situation that established a low accumulation point at the end of a system intended to accumulate and shed water is a sump.
  • Interior sumps that have been engineered and installed within the lowest level of a building. These types of sumps can range from the small sump capacity of only a few gallons to large commercial sumps that are designed to accumulate thousands of gallons of water, waste or other liquid.

If the sump is designed to drain on it’s own, by gravity, such as a drywell or a positively pitched discharge line out of the sump, then there is no need for a pump. If the sump is lower than the designed discharge elevation, then a pump is required. Therefore we have a sump pump.


There are several different ways to install a residential sump pump, however, it is best to understand the needs of the specific pump location, as well as the capacity that this pump should be anticipated to pump as discharge.

Specifically focusing on the residential use of the sump pump there are basic observations that can be made by the property owner to determine if a sump pump will improve the moisture conditions within the basement space.

  • If the lowest elevation of the property (the basement in most residential homes), shows occasional moisture build up on the foundation walls and no actual accumulation of water on the floor of the basement, then the need for an internal sump pump is probably not going to solve the problem. Moisture on the foundation walls is either caused by condensation within the interior space of the basement which is a humidity issue or water accumulating on the exterior of the walls. Resolution of the humidity situation is the control of moisture within the basement space. Dehumidifiers are recommended to accomplish this control.

If humidity is not the issue and the walls are wet either all the time or when there is a rainstorm, the following is probably occurring.

Water is building up on the exterior of the foundation wall and the hydrostatic pressure of the water as it accumulates against the sides of the exterior foundation walls, eventually finds its way through the foundation walls, and causes moisture buildup against the exterior walls. The installation of a sump pump within the basement space will probably not solve this issue.

The solution to foundation wall moisture is exterior waterproofing, drainage board and a full perimeter foundation drain system. This type of solution is presented in another discussion entitled How to Solve Foundation Wall Moisture Problems .


  • If the basement is showing an accumulation of standing water and the foundation walls are not the obvious reason, then the water is entering the basement from a level lower than the top of the basement slab. If this is the case, the installation of an interior sump pump will offer a solution to the problem.

Once it has been established that the water is not entering the basement space by an elevation higher than the top of the slab, floor elevation, the installation of a sump pump is recommended.

Read How to Install a Sump Pump

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