Overflow pool or skimmer pool: how the two systems differ

A channel runs around the perimeter under a grating, and the collected water drains to a balance tank. The pump draws from that tank, sends the water through the filter and returns it to the pool.

Because the whole surface is swept continuously, surface debris flows into the channel by itself. The 'line building up on the surface' seen in skimmer pools does not form in an overflow system. The waterline also reads as one continuous line, with no visible gap between the pool edge and the water.

The balance tank is the heart of the system. When someone enters the pool, the displaced volume goes to the tank; when they leave, it returns. Tank volume is sized from surface area: roughly 60 to 80 litres per square metre. For a 50 square metre pool that means a separate 3 to 4 cubic metre vessel.

Each of them lands on both the material and the labour side of the budget.

The plant room grows too. A skimmer system needs 4 to 6 square metres for the pump and filter, while in an overflow system with a balance tank added, that area increases. The mistake we correct most often on villa projects is choosing an overflow system and leaving the plant room at skimmer size.

The external dimensions of the pool change as well. The overflow channel and grating add 40 to 50 cm to the pool's outer dimensions around the perimeter. On projects close to the plot boundary, this difference is large enough to affect the permit. Do not decide the size before you have chosen the system.

This lowers chemical consumption somewhat. On the other hand, because the water surface in contact with the open air and the channel volume are larger, water loss from evaporation is slightly higher.

In a skimmer pool, surface cleanliness depends on the wind and on skimmer placement. With the right number of skimmers in the right positions the result is trouble-free; in pools fitted with too few skimmers, a line forms on the surface and the robot cleaner has more work to do.

In terms of heating there is no decisive difference between the two systems; heat is lost through the water surface, and the surface is the same in both. In either system, a pool cover is the investment that pays back fastest.

It delivers the same water quality for a smaller investment; the difference lies in appearance, and not everyone needs to pay for that.

Villas facing a view, projects that call for an infinity edge, hotels and commercial facilities are built with an overflow system. In hotel pools under heavy use, a surface that cleans itself is a real advantage for the operation.

For competition pools there is no debate: an overflow system is mandatory. The water flows from the edge into the channel so that the wave a swimmer creates does not hit the wall and bounce back. On Olympic and semi-Olympic pools this is not a preference but part of the standard.

One edge of the pool has no coping; the water falls from that edge into a catch basin below and from there goes to the balance tank.

The other three edges can be skimmer or overflow. We build solutions with an infinity edge on the view side and skimmers on the remaining edges; compared with a full overflow system, this gives a similar look on a more measured budget.

An infinity edge needs a slope in the land. On a flat garden an infinity pool produces no effect, because there is no change in level behind the spill edge to break the line of sight. If there is no slope, spend the money elsewhere.