Overflow Swimming Pools — How They Work and When They Suit
In an overflow swimming pool the water sits level with the deck and spills continuously over the edge into a hidden gutter. The result is a mirror-flat surface and very clean surface water — but it depends on a gutter, a grating, a balance tank and precise levels that a skimmer pool does not need. This guide explains how overflow and infinity edges work, when they are worth it, and what they need to stay that way.
How an overflow pool works
In a skimmer pool, water is drawn off through skimmer openings in the wall a little below the coping. In an overflow pool the pool is filled to the brim: water spills over the edge into a perimeter gutter, flows by gravity to a balance tank, and is pumped from there through the filter and back into the pool through inlets usually set in the floor.
Because the whole surface layer — where leaves, dust, oils and sunscreen collect — is skimmed continuously along the edge, the surface water stays cleaner, and returning filtered water through the floor distributes it evenly through the pool.
The parts of an overflow system
Perimeter gutter
A channel built into the structure around the pool edge, laid to falls towards its outlets, waterproofed together with the pool shell, and sized for the water that flows over the edge when the pool is in use.
Grating
The removable grille that covers the gutter and forms the walking edge. It has to be slip-resistant, strong enough to stand on, safe for fingers and toes, stable in sunlight, and easy to lift for cleaning.
Balance tank
A buffer tank, usually below deck level, that absorbs the water pushed out when bathers get in, holds the water draining from the gutter, and supplies water for backwashing. It carries the automatic top-up and level control, and it needs access for cleaning.
Floor inlets and controls
Filtered water returns through inlets in the floor, while level sensors and a top-up valve keep the balance tank in its working range so the pump never runs dry.
Infinity and vanishing edges
An infinity edge is a variation of the overflow principle. Instead of a gutter all round, one or more sides are built slightly lower than the rest; water slips over that edge into a catch basin below and returns from there to the filter. From the right viewpoint the water appears to run straight into the view beyond — the sea, a garden or the horizon.
It only works where there is a view and a level difference to accommodate the catch basin, and the weir must be level to within millimetres along its whole length — otherwise water runs over one end and leaves the other dry. Wind, and the sound of falling water, need to be considered at design stage.
Overflow vs skimmer
- Look — overflow puts the water flush with the deck; a skimmer pool leaves a visible strip of wall above the waterline.
- Water quality — overflow skims the whole surface continuously; a skimmer draws from a few points, which is enough for most private pools.
- Structure — overflow needs a gutter, a balance tank and more precise levels; a skimmer pool does not.
- Plant room — overflow needs more space for the balance tank and larger pipework.
- Running — overflow circulates more water and loses more to evaporation, so pumping and top-up water are higher.
- Cost — the gutter, grating, balance tank, pipework and precision make overflow the more expensive option to build and to run. See what drives pool cost.
When an overflow pool suits
Overflow is worth it when the look matters most — a modern villa, a terrace with a view, a hotel or a club — and in pools with a heavy bather load, where skimming the whole surface keeps the water clearer. It is less suited to a tight plot with no room for a balance tank, to a project where budget is the main priority, or to an exposed site where wind-blown sand will settle in the gutter constantly.
Construction details that make or break it
- The overflow edge set level to within millimetres along its whole length — checked with an instrument, not by eye.
- Gutter and balance tank waterproofed as part of the same system as the pool shell.
- Gutter falls and outlets sized for the flow when the pool is full of bathers.
- A balance tank sized for bather displacement, gutter water and backwash, with access for cleaning.
- Pipework and pumps sized for the higher circulation of an overflow system.
Maintaining an overflow pool
- Lift and clean the grating and flush the gutter regularly — leaves and sand collect there first.
- Clean the balance tank periodically and make sure sludge is not reaching the pump.
- Check the level sensors and top-up valve so the balance tank stays in range.
- Watch evaporation: overflow pools lose more water, and topping up with hard water increases scaling on the edge.
- Remove scale lines along the overflow edge before they become permanent.
Our guide to pool maintenance in Egypt covers routine servicing in more detail.
Overflow pools by Fox Pools
Fox Pools builds both overflow and skimmer pools, in concrete and as prefabricated systems, and has done so in Egypt since 1993. The edge, gutter and balance tank are designed with the structure and the waterproofing from the start, and circulation is sized to the actual volume.
Our concrete pools carry a structural warranty of up to 10 years. The pumps, sand filters, multiport valves, LED lights and fittings we install are made by our sister company Waterstar in Badr City, and every component is available as a spare part.
Overflow swimming pool FAQs
What is the difference between an overflow pool and an infinity pool?
In an overflow pool the water spills over the edge on all sides into a perimeter gutter. An infinity pool lets water spill over one or more chosen edges into a catch basin below, so the water appears to merge with the view. Both rely on a balance or catch tank.
Why does an overflow pool need a balance tank?
The balance tank absorbs the water displaced when people get in, holds the water draining from the gutter, supplies backwash water and keeps the pump fed. Without it the pool would overflow when used and run the pump dry when not.
Does an overflow pool cost more to run?
Usually, yes. It circulates more water, needs larger pipework and pumping, and loses more water to evaporation along the overflow edge, so electricity and top-up water are higher than for a comparable skimmer pool.
Can a skimmer pool be converted to overflow?
It is a major renovation: cutting down the edge, building a waterproofed gutter, adding a balance tank and replacing pipework. It is sometimes possible and is assessed case by case at survey. See our guide to pool renovation.
How often should the gutter and grating be cleaned?
Whenever debris builds up, and more often on exposed, windy or sandy sites. Regular cleaning of the grating, gutter and balance tank keeps the flow even and stops debris reaching the pump.
Considering an overflow or infinity edge?
Share your site, the view and how the pool will be used. An engineer will review whether an overflow or infinity edge suits it and prepare an itemised quotation.