The infinity edge
The infinity edge — also called the negative edge or vanishing edge — is the most widely recognised overflow configuration. Water spills continuously over one or more sides of the pool, creating the illusion that the water surface extends to the horizon.
The overflow weir is formed by the top of the pool wall on the overflow side, finished with a precision bevel at water level — no coping is laid on this side, as the bevelled wall itself forms the weir over which the water spills. On the remaining sides, the structural wall rises approximately 3 cm above the water surface, and the coping is bonded to this higher arase — giving a visible edge 3 cm plus the coping thickness above the water surface.
The bevel is not a decorative choice. A flat-topped wall remains visible beneath the water sheet, breaking the visual continuity of the overflow effect. It also presents a safety risk — a flat surface invites people to step on it, and a fall on the gutter side can be serious.
The infinity edge works best on sloped sites with a clear view — the vanishing line reads against the landscape or the sky, amplifying the visual effect.
The under-coping overflow
In an under-coping overflow, the water level sits less than 1 cm below the top of the structural wall. The coping overhangs the pool edge slightly, concealing the overflow channel beneath it. The water disappears under the coping rather than spilling visibly over it.
With a standard 2 cm coping, the water surface sits less than 3 cm below the visible walking edge — almost imperceptible from the terrace level. The overflow effect is discreet: the pool reads as flush with its surroundings without the dramatic vanishing line of an infinity edge.
This configuration is often chosen for urban settings, enclosed gardens or projects where the pool is viewed from the same level rather than from above or at a distance. The hydraulic principle is identical to the infinity edge — water spills into a gutter and flows to the balance tank — but the visual expression is more contained.
The zero edge
The zero edge — also called the ‘deck level pool’ — takes the overflow concept to its logical extreme: the water surface is at the same level as the surrounding terrace. There is no coping, no visible edge, no transition between the pool and the deck. The water and the walking surface are coplanar.
This configuration requires precise management of the terrace levels surrounding the pool. A system of imperceptible slopes and counter-slopes directs the overflowing water towards the overflow channel below – pool edge details that must be resolved in the design drawings before any groundwork begins.
The zero edge is the most demanding overflow configuration to execute correctly. The structural wall, the terrace finish and the drainage system must all be designed together, with tolerances measured in millimetres. It is also the most visually powerful – particularly for flat sites or rooftop installations where the pool surface and the terrace read as a single continuous plane.
Edge finish and materials
Across all three overflow configurations, the choice of edge finish affects both the visual result and the long-term performance of the overflow weir.
Natural stone – granite, limestone, and travertine – is the most common choice for overflow pool edges. Its density and low porosity make it durable in pool water conditions, and its weight helps maintain the precision level of the weir. The finish of the underside of the coping matters: a rough or uneven surface creates drip points that break the water sheet. A smooth, consistent underside allows the water to follow the stone and fall cleanly.
For zero-edge pools, the terrace finish and the pool lining must be specified together — the junction between the two surfaces is the most technically demanding detail of the entire project.
Pool fittings at the overflow edge – level sensors, water supply connections – should be positioned and sized to avoid interrupting the water sheet. Their location is determined in the hydraulic drawings, not after the coping is laid.
Morana's advice
The overflow edge type is one of the first decisions in a pool project — and one of the most consequential. It determines the structural wall geometry, the coping specification, the gutter design and the balance tank sizing. Changing it mid-project means redesigning the structure.
We specify the overflow edge configuration as part of the preliminary design, resolved in section drawings before any groundwork begins. The result is a water line that performs exactly as designed — on day one and over the long term.
For a complete overview of how an infinity pool works – from hydraulic circuit to balance tank and filtration – see our infinity pool construction guide.”