Pools with an overflow system are the most modern. The system works as follows: water from the pool enters the overflow channel where it is directed into a reservoir, then the water goes through a filtration system and flows back into the pool. Excellent circulation helps clean large amounts of water all at once.
This system requires: an overflow reservoir (replacing the skimmer), overflow gutters and grids to cover the gutters. The overflow system has a more complex design therefore such pools are more expensive than normal ones.