Infinity-edge pools: what they really require, and why they cost double

The infinity edge is sold as a finish and bought as a finish: the same pool, but with one side left open so the water merges into the landscape. Hence the question that always comes — "how much more does it cost?" — and hence the surprise, because the answer is not in the wall.

An infinity-edge pool is not a pool with a different edge. It is a pool with a different hydraulic system, and since May 2026 that has stopped being an engineer’s opinion and become something written into a rule.

First, which family we are talking about

There are two ways of taking dirty water off a pool, and price, maintenance and appearance all follow from which one is used. It is worth getting the names straight before going on.

And here is the first point of law that surprises many people: an infinity-edge pool has no skimmers. The resolution requires one skimmer per 46.5 m² of water surface, or a perimeter overflow system for surfaces larger than 312 m², and then closes the numeral with a single sentence: "This does not apply to infinity-edge pool tanks".

The rule that changes everything: the pump does not draw from the floor

If you take only one idea from this article, take this one. In an ordinary pool the pump draws from the floor and from the skimmers, filters, and returns. In an infinity-edge pool it does not:

Read it slowly, because it inverts the intuition. All the flow the pump moves has to leave over the top of the wall. The water falls into the overflow channel, runs by gravity to the surge tank, and it is from there — not from the shell — that the pump takes its water. The floor drains are left as a dead leg that is only opened on the day the pool has to be emptied.

Almost every economic consequence of the infinity edge follows from that inversion. The surge tank stops being an accessory and becomes the thing the pump depends on for water. If the tank is undersized, the pump draws air; if it overflows, you are throwing treated, heated water down the drain.

The surge tank, and an ambiguity in the rule

The surge tank is a second vessel, normally buried next to the plant room, that absorbs everything the shell itself absorbs in an ordinary pool: the water in transit at any moment over the wall and along the channel, the volume bathers displace when they get in, and the water that runs back by gravity when the pump stops.

The rule makes it compulsory and gives it a minimum size:

There is a drafting problem here worth declaring rather than settling on our own account: the rule says "or", and does not say which of the two governs when the two do not give the same answer. And in an ordinary domestic pool they are nowhere near the same.

The arithmetic, for a pool of 8.00 × 4.00 m and 1.50 m average depth, which is 48 m³ of water and 32 m² of water surface:

The tank also needs its own instrumentation, which is the item forgotten straight after the tank itself: level probes — high, low and cut-out —, automatic make-up with its valve and meter, and a low-level cut-out that stops the pump before it runs dry. Without that cut-out, the first day the make-up fails you lose the mechanical seal.

The weir wall: millimetres, not centimetres

This is the part no rule governs and the one that decides whether the pool looks right or looks wrong, so I say it as what it is: site judgement.

The visual effect of an infinity edge depends on the water sheet falling at a uniform thickness along the whole length of the wall. And the thickness of that sheet, in a domestic pool, is a few millimetres. Which means that if the top of the wall is three millimetres out of level, it shows: a curtain falls at the low point and nothing falls at the high one.

That is why an infinity edge is not set out with a water level or finished by eye. It is levelled with an instrument, checked with the shell full before tiling, and the weir finish is executed once the structure has settled. A wall corrected afterwards with mortar produces exactly the defect it was meant to avoid.

The structure: two problems an ordinary pool does not have

NSR-10 does concern itself with pools, whatever people repeat to the contrary. Title B, dealing with uplift, says expressly that "the same consideration must be given to the design of tanks and pools" and refers to Chapter C.23, entitled "Tanks and environmental engineering concrete structures", which covers, in those words, "pools and basins forming part of the equipment of buildings".

Two things in that chapter weigh especially on an infinity edge:

1. 1An empty shell floats. C.23 requires uplift on empty tanks to be taken into account and ballast to be provided against flotation failure. An infinity edge is usually built on a slope, with the wall high on the outside and groundwater or run-off behind it: this is precisely the situation in which emptying the pool for maintenance is the moment of greatest structural risk, not the least.
2. 2Watertightness is tested, and it goes on the drawings. The same chapter requires drawings and specifications to include the requirements for testing impermeability and watertightness before the surrounding backfill is placed. It is not good practice: it is compulsory drawing content. If your drawing set does not carry it, the set is incomplete.

To which must be added that the weir wall is, structurally, a retaining wall with water on one side and air on the other, and that in most cases the ground falls away just behind it. The definitive geotechnical study, which NSR-10 makes compulsory for every urban and suburban building with no size threshold, is no formality here: it is what says whether the wall needs piles.

The surround that has to be made up elsewhere

A detail of the rule that changes the layout and that almost nobody allows for when drawing. Perimeter surrounds must be at least 1.20 m wide measured from the edge of the pool, falling 3% to 5% towards the drains. And the infinity edge, by definition, eats that surround on the side it spills over.

The resolution allows it, but on two conditions: an infinity-edge or falling-overflow design is accepted on up to 50% of the perimeter, and the surround area not built must be made up on the sides where it is built, mitigating the risk of overbalancing or falling to another level.

On a tight plot that is what decides the size of the pool, and it gets discovered late: the water surface that fits is drawn first, and then the made-up surround the rule asks for on the other side does not fit.

What it costs every month, which is also more

The extra cost of an infinity edge does not end on handover day. Three running costs go up, and they go up for physical reasons:

• —Make-up water. A sheet falling as a curtain evaporates far more than a still surface, and the wind carries part of the water outside the channel. Make-up stops being a trickle and becomes a budget line.
• —Chemicals. All the water replaced comes in untreated and has to be treated. More make-up is more chlorine and more pH corrector, in the same proportion.
• —Energy. The system has to move 100% of the flow over the top of the wall, which means overcoming the height of the weir continuously. The pump does not switch off between bathers: if it does, the edge stops existing and the pool looks like any other.

And one that costs no money but costs goodwill: noise. A curtain of water falling a metre into a concrete channel makes a sound, and it makes it all night if the pump is timed to run at night. At a country house it is usually pleasant; next to a bedroom, not always. It is solved through the height of the fall and the finish of the channel floor, and it is solved at design stage.

Why it costs double: the six items

Put together, the extra cost of an infinity edge over the same pool with skimmers is made up of this, and of nothing else:

1. 1The weir wall, with its crest levelled by instrument and its finish executed as a second stage.
2. 2The overflow channel: a waterproofed concrete channel, with its fall and its grating, which does not exist in a skimmer pool.
3. 3The surge tank: a second watertight structure, buried, with its own waterproofing and its own access.
4. 4The level instrumentation: probes, automatic make-up, low-level cut-out and its controls.
5. 5The structure, when a high wall on a slope calls for special foundations or ballast against flotation.
6. 6The made-up surround on the sides that do have one, which may force the water surface to shrink.

None of the six is a contractor’s whim and five of the six are now in the rules. When somebody offers you an infinity edge "for a little more", the question that settles the conversation is short: where is the surge tank in your quotation, and what size is it? If it is not there, what you are being quoted is not an infinity edge: it is a lower wall.

What does not change

It is worth closing with this because it gets asked often. The infinity edge exempts you from nothing else: the two submerged drains at least 0.90 m apart still apply, hydraulically balanced, with anti-entrapment cover, vacuum release system and emergency stop button — even though those drains are only used for emptying — and Ley 1209 still applies in full.

In particular, the infinity edge does not replace the enclosure. It is a mistake that turns up now and then in handsome projects: because the water merges with the landscape, it gets drawn without a barrier. If the pool is of restricted use — the residential development, the club, the hotel — an enclosure with access control is compulsory and there is no aesthetic exception. What the law asks for and what it does not is in Ley 1209: what it really requires.

Where this comes from

Whoever leads this line of work in the studio brings fifteen years of designing hydraulic systems and bodies of water, and between 2019 and 2022 built infinity-edge pools, spas and waterfalls with the systems behind them — pipe networks, filtration plants, pumps and plant rooms — in the Bahamas, Bermuda, Turks & Caicos and Miami.

From which comes the warning I will close on. In an infinity edge, what you see is a wall; what decides whether it works is buried behind it. And unlike almost everything else on a building site, that cannot be added later.