Overflow pool or skimmer pool: how the two systems differ

In an overflow pool the water sits flush with the coping and spills over the edge continuously. 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 top layer is removed around the whole perimeter, the surface cleans itself. The waterline film that forms in skimmer pools does not build up. The water edge reads as one continuous line, with no visible gap between coping and 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.

Five items come with the overflow layout: the balance tank, the perimeter channel and grating, level control automation, a longer pipe run and a higher duty pump. Each of them lands on both the material and the labour side of the budget.

The plant room grows too. A skimmer pool for a private house works with 4 to 6 square metres at a clear height of no less than 1.80 metres. Once a balance tank is added, that area increases. The mistake we correct most often on villa projects is an overflow system specified against a plant room sized for skimmers.

External dimensions change as well. The channel and grating add 40 to 50 cm around the perimeter. On plots where the pool already sits close to the boundary, that difference is large enough to affect planning consent. Decide the system before you fix the pool size, not after.

In an overflow pool the surface renews constantly, so oils, sun creams and dust leave quickly. That offsets part of the chemical consumption. Against it, the water area in contact with air and the channel volume are both larger, so evaporation losses run slightly higher.

In a skimmer pool, surface cleanliness depends on wind direction and skimmer placement. With the right number of skimmers in the right positions the result matches an overflow pool in practice. Where skimmers are under-specified, a waterline mark forms and the robot cleaner works harder.

Heating is effectively the same in both. Heat leaves through the water surface, and the surface area is identical either way. A pool cover pays back faster than any other item on both systems.

For a family swimming in their own garden, a skimmer pool is enough and it is the sensible choice. It delivers the same water quality for a smaller outlay. The difference between the systems is largely visual, and not every client needs to pay for it.

Villas with a view, projects with an infinity edge, hotels and commercial sites are built as overflow pools. Under heavy hotel use, a surface that clears itself is an operational gain rather than a cosmetic one.

For competition pools there is no discussion: overflow is required. The wave a swimmer creates has to leave through the channel instead of bouncing back off the wall into the lane. On Olympic and short course pools this is part of the standard, not a preference.

An infinity pool is an overflow system applied to one edge for visual effect. That edge has no coping; the water falls into a catch basin below and travels from there to the balance tank.

The other three sides can be skimmer or overflow. We often build the view side as an infinity edge and keep the remaining sides on skimmers, which produces a similar picture on a more measured budget.

The effect needs a change in ground level. On a flat site the eye finds no drop behind the spill edge and the illusion does not read. Where there is no fall, that money does more work in the finish or the surrounding deck.

For either system: pump duty in cubic metres per hour, filter diameter, pipe diameter, plant room area required, and the return inlet layout. Return inlets are the most overlooked part of a pool; if they do not set up a circular flow, dead zones form in the corners and algae starts there.

For an overflow system specifically: balance tank volume and where it sits, channel and grating type, and how level control is handled. Ask whether the tank is inside the plant room or adjacent to it, because that answer changes the excavation.

Get all of it in writing. A quotation with a pool drawing but no hydraulic schematic is telling you that half the job will be improvised on site.