A surge tank is a water containing vessel that takes water from a swimming pool perimeter gutter system. Swimmers create waves when they enter a pool, compete, swim laps, exercise or just play. The perimeter gutter system captures 
these waves, or surge of water, so that they do not rebound back into the pool. A perimeter gutter and surge tank system are important in that they assist competition pool water, or any pool with a gutter system, return to a quiescent state which is a faster pool. Competition or training pools that do not utilize a gutter and surge tank system are slower and antiquated.
Surge tanks are typically constructed of concrete and located in the filter room or under the pool deck adjacent to the swimming pool. Cast-in-place concrete allows the swimming pool designer to size the surge tank as needed to fit the site conditions. Pre-cast surge tanks can be used as well but the dimensions tend to be less flexible. The surge tank size depends upon the surface area of the swimming pool. Most local and state health codes require one (1) gallon of surge capacity for every one (1) sq ft of pool surface area. Only a few health codes require two (2) gallons of surge capacity for every one (1) sq ft of pool surface area. This should be confirmed with local or state health department regulations.
There is a lot going on inside a surge tank. Piping from the perimeter gutter to the surge tank enters at several 
locations. The number of gutter dropouts depends on the size of the pool. Main re-circulation piping pulls water from the surge tank to the re-circulation pump and filter system before it is chemically treated and returned to the pool. Special consideration is also needed for maintaining atmospheric pressure inside the vessel. Typically, an air relief vent pipe is satisfactory for maintaining this equalization. However, the vent line should be routed independently to atmosphere to ensure that noxious fumes and vapors from the surge tank are not introduced into the filter room or natatorium. A water level controller should be installed in the surge tank as well to monitor the water level and automatically activate the automatic water make up control valve should the water level drop below design levels. An access hatch is always required to access the interior of the surge tank for cleaning and routine maintenance. When surge tanks are constructed under the pool deck adjacent to the pool, they are usually placed next to the deep end of the pool. This approach saves on construction cost as one wall is common with the pool.
Surge tanks are installed on the fastest swimming pools in the world including Olympic Venues, Universities, High Schools, Elementary Schools and Municipal Aquatic Facilities. If your aquatic facility has a competitive pool, training pool or lap pool and a fast pool is desired then you will want a perimeter gutter system complete with a surge tank.