Pool edges explained: skimmer, deck-level overflow and raised

Three ways to end a pool

Every pool has to stop somewhere, and there are only three honest answers to where the water ends relative to the ground you walk on: below the deck, level with it, or above it. Those are the skimmer pool, the deck-level overflow pool and the raised pool — and nearly everything else about the build follows from which one you pick.

The choice is not only aesthetic. It sets how the water is cleaned, how much structure goes into the ground, what stands in the plant room, and how the pool behaves when eight people get in at once. It is also close to irreversible: turning a skimmer pool into a deck-level one later means rebuilding the wall tops, the deck and the pipework.

So decide it early, before the shape, the finish or the steps. Nothing else in the build casts as long a shadow.

Skimmer pools: the pragmatic default

In a skimmer pool the water sits about 15 cm below the deck, and wall-mounted skimmer units draw the top few centimetres into the filter. That gap is the freeboard, and it does real work: it absorbs the wave when somebody jumps in, swallows splash, and stops rain running off the deck straight into the pool.

The structure is the simplest and cheapest of the three: no perimeter channel, no balance tank, standard coping, and a level tolerance in centimetres rather than millimetres. One skimmer serves roughly 25 m² of surface, so an 8 × 4 m pool takes two. Put them on the wall the prevailing wind blows toward, so the breeze delivers the leaves, and put the return inlets opposite, angled to set up a slow rotation.

The trade-off is the look and the housekeeping. You see the waterline band, so the pool reads as set into the deck, and that band collects a greasy tidemark somebody has to wipe. Skimming also stops when the pump stops: with the filtration off, whatever is floating stays there.

Deck-level overflow: the water becomes the floor

In a deck-level pool the water stands flush with the deck and spills continuously over the whole perimeter into a hidden channel — a grated gutter, or a narrow slot in the coping. From there it runs to a balance tank, through the filter, and back into the pool, usually through floor inlets that push clean water up through the full depth.

Two things make it worth the money. The entire surface skims itself for every minute the pump runs, so dust and pollen never get the chance to settle — which is why public pools are built this way in many countries. And visually the pool becomes a sheet of water set into the terrace: mirror-flat, with no waterline band at all.

The demands are real. The rim has to be level to a few millimetres the whole way round, or the water spills unevenly and the eye catches it at once. The balance tank holds roughly 5–10 % of the pool volume, because every swimmer displaces water that has to go somewhere. And it only looks right while the pump runs: switch it off and the level drops into the channel.

A skimmer pool is a pool with a waterline; a deck-level pool is a floor made of water — every other difference between them follows from that one sentence.

Raised pools: architecture above the ground

A raised pool lifts its rim 40–60 cm above the deck. At that height the edge becomes seating — bench height, more or less — and the pool becomes an object in the garden rather than a hole in it. On a sloping site it is often the cheapest route to a level pool, because part of the depth is achieved by building up instead of digging down.

It brings two quiet advantages. A 45 cm wall is a genuine barrier to a toddler, and it stops grass clippings, leaves and garden dirt being walked or blown straight into the water. It also saves excavation, which on rock or a high water table matters a great deal.

The cost simply lands somewhere else. Every visible face wants stone, tile or timber, and cladding a 45 cm band around a 24 m perimeter is not a rounding error. The wall also has to resist water pressure without soil bracing it, so it is thicker and more heavily reinforced than a buried one.

What each edge does to the water

Cleanliness follows geometry. A skimmer draws water from two or three points on one or two walls, so it depends on the wind and on well-aimed return inlets to bring the debris to it. A deck-level edge draws from every metre of the perimeter at once, so nothing collects in a corner.

In practice, a well-set-up skimmer pool with correctly angled returns is clean and undemanding. A deck-level pool is cleaner with less thought, noticeably so under trees or in pollen season. A raised pool is, hydraulically, just a skimmer pool that happens to stand up — unless one wall is built as a weir.

There is a water-loss difference too. Deck-level pools lose a little more to splash-out, with no freeboard to catch the wave. The balance tank's filling valve hides the extra top-up, which is why you should read the water meter now and then.

Where the money actually goes

Take the skimmer pool as the baseline. A deck-level edge typically adds 15–30 % to the shell: the perimeter channel and its grating, the balance tank, extra pipework and a larger pump — plus precision, meaning levelling, waterproofing and tiling to a tolerance a skimmer pool never asks for.

A raised pool trades excavation for cladding. You dig less and finish more, so on a flat, easily dug site it usually costs a little more than in-ground, and on a slope or in rock it can cost less. The swing is almost entirely the cladding material.

Running costs differ too, though less dramatically. A deck-level pool wants longer pump hours for the edge to look right. Against that, its surface is cleaner, its chemistry steadier, and less debris reaches the floor for the robot to chase.

Hybrids, and the infinity edge

The three systems are not a strict either-or. An infinity edge is simply a one-sided overflow: one wall lowered to a precise weir, water sheeting over it into a catch basin, the other three sides built as an ordinary skimmer pool. It needs a view or a drop behind it to be worth anything, and the same balance tank as a full overflow.

Other mixtures earn their keep. A raised seat wall along one long side of an otherwise in-ground pool gives you the bench without cladding four faces, and a raised end wall can double as the bench that hides the cover roller.

What does not mix is precision and improvisation. Any overflow edge — full, partial or infinity — needs a laser, a drawing and a builder who has finished one before. This is not the part of the project to learn on.

How to choose, and how to see it

Three rules cover most cases. If the pool is a family tool and the budget is finite, build a skimmer pool and put the difference into heating and a cover. If the pool is part of the architecture — or small enough that the perimeter premium stays modest, as on a plunge pool — the deck-level edge is the upgrade with the biggest visible payoff. If the site slopes, if there are toddlers, or if the pool has to read as furniture in a courtyard, raise it.

Then look at all three on your own pool. In the designer the edge system is one click, and the whole structure follows: water level, coping, gutter details, even where the skimmers sit. Switch between them at your real dimensions and the choice usually makes itself.

What goes wrong in practice

1. Choosing the edge after the shell is designed

   Every edge system changes the top of the wall, the deck build-up and the pipework. Retrofitting an overflow channel means rebuilding the perimeter. Decide first, and every later detail has an easy answer.

2. An overflow pool without the plant room to run it

   The channel, the balance tank and the bigger pump need space and a competent installer. An overflow built on a skimmer pool's budget gives you an uneven edge and a tank that runs dry — the worst of both systems.

3. Skimmers on the wrong wall

   Placed upwind, they fight the breeze all summer while debris gathers in the far corner. Put them where the wind pushes the surface, and aim the return inlets to help rather than to look tidy.

4. Forgetting to clad the raised walls

   The structure gets built and the stone gets postponed, and the pool spends its first season as a grey concrete box in the garden. Price the cladding at the same time as the shell.

5. Expecting a deck-level pool to look right with the pump off

   The mirror surface exists because water is spilling. Cut filtration hours to save money and the level drops into the channel, taking the whole effect with it.