Infinity and deck-level pools at home

Two different pools with one reputation

Almost everything sold as an infinity pool for a private garden is one of two things, and they are not the same. An infinity pool, strictly, has one wall lowered to a weir: water sheets over it into a catch basin below, and from the right viewpoint the surface merges with whatever lies behind — sea, valley, sky. A deck-level pool overflows on every side into a hidden channel, stands flush with the terrace, and reads as a mirror set into the paving.

Hydraulically they are one family: water leaves over an edge, is caught, buffered and pumped back. Visually they answer different sites. The vanishing edge needs a drop and a view to vanish into. The deck-level pool needs nothing but a level terrace, which is why most gardens should be building that one — and why most of the photographs people fall in love with are in fact of it.

The vanishing edge only vanishes from one place

This is the part nobody mentions. The effect works when your eye is at, or slightly above, the plane of the water and the horizon behind lines up with the weir. Stand in the pool, or sit on a terrace at the same level, and the water runs off into the landscape. Walk ten metres uphill and you see the trough, the wet wall and the plumbing. A vanishing edge is an effect designed for a viewpoint, so choose the viewpoint first — from the kitchen, from the loungers, from the water — and set the weir height to it.

That also settles which wall it goes on: the side facing the drop, at the end of the axis you arrive along, and ideally with nothing built behind it for a long way. An infinity edge pointed at a hedge three metres away is a very expensive waterfall.

What the edge needs below it

Under the weir sits the catch basin, and it is wider than people expect. The film does not fall straight down; it curves outward, and wind carries it further. As a rule, make it at least a third of the fall height wide, never less than 45–60 cm, and more on a tall edge. Too narrow and the pool throws water into the garden every windy afternoon, the level drops, and the automatic top-up runs quietly all season.

The basin drains to a balance tank — a buffer of roughly 5–10% of the pool volume, with level sensors, automatic filling and an overflow to drain. It absorbs everything: the water standing on the weir, the displacement of four people getting in at once, rain, evaporation. It needs an accessible home, usually in or beside the plant room, and it belongs in the drawings early, because it is a structure rather than a fitting.

A vanishing edge vanishes from exactly one viewpoint — if that is not where you will be standing, you are paying for a photograph you are not in.

Flow: the edge is a second circuit

A film thin enough to be silent still needs real flow — roughly 2 m³/h per metre of weir for a wet, quiet edge, and 4–6 m³/h per metre for a visible, audible sheet. On a 5 m edge that is 10–30 m³/h moving purely for the effect, on top of the filtration circuit.

Run it as its own pump, not as a share of the filter pump. Two jobs on one pump means the edge stutters as the filter loads up and disappears entirely during a backwash. A variable-speed edge pump pays for itself twice: you can tune the film to the exact thickness that looks right, and run it quietly on a low setting when nobody is watching.

Level, structure, and why the builder matters

The weir has to be level to within about 3 mm along its whole length. Water finds any low point immediately and turns a sheet into a stripe, and there is nothing to hide it with afterwards. That tolerance has to survive the concrete, the waterproofing and the finish, so put it in the contract as a number and have it checked with a level instrument before the edge is tiled.

It has to survive the ground too. A vanishing edge usually sits at the top of a slope, the least stable place on the plot: the weir wall wants its own foundation carried down to competent ground, sometimes piles, and the retaining structure under the basin is often the largest single item in the build. A few millimetres of settlement are invisible in an ordinary pool and fatal in this one. This is the pool where you choose the builder on references, not on price.

Deck-level: slot or grate

On flat ground the same hydraulics give you the mirror, and two details decide everything. A grated gutter — 15–25 cm wide with a removable grate — takes more flow, forgives a slightly less perfect level and is easy to clean, but it reads as technical: you see a band around the pool. A slot is 12–25 mm wide, disappears completely and makes the water look poured into the terrace, but it demands a perfect level, collects leaves you have to fish out, and handles less flow.

Both give the best water quality of any edge system, because the whole surface is skimmed continuously instead of being dragged toward two skimmer mouths. And the cost follows perimeter rather than area, which is why a deck-level plunge pool is such good value: 13 m of channel around a 4 × 2.5 m pool, against 24 m around an 8 × 4 m one.

What it costs, and what it costs to run

A deck-level edge typically adds 15–30% to the shell compared with a skimmer pool: the perimeter channel, the balance tank, the second pump, the extra pipework and more demanding waterproofing. A hillside infinity pool can be well beyond that, and usually not because of the edge itself — it is the retaining structure, the access for machines and the excavation on a slope that move the number.

Running costs are honest and moderate: the edge pump's electricity when you want the effect, and slightly higher evaporation from the moving film. The bigger recurring item is attention. Scale shows on the weir first, because that is where water evaporates fastest, so keep pH and calcium hardness in range or you will be descaling the one surface everybody looks at.

Living with one, and how to decide

The edge is a switch, not a condition. Turn the pump off and the water settles level with the weir, still and mirror-flat; the effect and the sound come back when you want them. In a frost climate the gutter, the balance tank and the edge lines all have to be drained and blown out before winter — ask how at the quotation stage, not in November.

Three questions decide it. Is there a drop, and a viewpoint that sees it? Do you have a builder who has done this before and can show you one that is five years old? Are you willing to pay both the premium and the attention? If any answer is no, build deck-level all round — or switch the same pool between skimmer, overflow and raised in the designer and see how much of the effect you actually give up.

What goes wrong in practice

1. An infinity edge with nothing behind it

   The effect is borrowed from the landscape. With a fence three metres away, all you have built is a wet wall and a pump bill; on flat ground a deck-level edge does the same job better.

2. An undersized catch basin

   The film curves outward and the wind takes it. Below about 45–60 cm the garden gets the water, the level drops, and the top-up valve runs all summer without anyone noticing.

3. One pump doing two jobs

   The edge stutters as the filter loads and dies during a backwash. Give the edge its own pump and its own pipework, and make it variable-speed so you can set the film.

4. Levelling by eye, or building on ground that moves

   A 5 mm dip turns a sheet into a stripe, and the water finds it on day one. Survey the weir, and found the wall properly where it sits on a slope.

5. Forgetting the frost

   A full gutter and a balance tank of standing water crack things that are expensive to reach. Plan the winter drain-down with the builder while the pipework is still on paper.