An overflow pool is also known as a deck level pool. The entire perimeter of the pool is surrounded by an overflow channel. The water line is level with the edge of the pool and overflows into this channel. The channel is typically covered with plastic grating. However, in high-end domestic pools, it is becoming more common to cover the drainage channel with tiles or stone for a luxury finish. This channel then leads into a balance tank. A balance tank is an additional holding tank that sits underground, below the pool level. Water from the overflow channel drains into the balance tank. This water is then fed into the filtrations system, before being pumped back into the swimming pool. The balance tank is typically made of concrete or plastic. It is capable of holding 15% of the total pool water volume.  Because of this, pools using an overflow or deck level system require a lot more room. And this needs to be considered in the planning and drawing stages. Once construction has begun, it is very difficult to change the pool design to incorporate an overflow design.