A backyard infinity pool looks like the water simply ends and drops into the view beyond it. There is no trick of the eye and no hidden glass. The effect comes from careful engineering tucked just out of sight.
Once you understand the parts involved, the vanishing edge stops looking like magic and starts looking like what it really is, which is precise construction.
Here is how a backyard infinity pool works, and why these pools take more skill to build than a standard one.
What a Backyard Infinity Pool Is
An infinity pool goes by a few names, including vanishing edge and negative edge. They all describe the same design. One wall of the pool is built slightly lower than the water level, so water flows over that edge without stopping.
When you look across the pool, the water seems to meet the horizon with no visible boundary. The effect only works when there is something to look at past the edge, such as a hillside, a valley, or a city skyline.
That is why these pools turn up so often on sloped lots where the land falls away behind the pool, and why they have become one of the most recognizable elements of luxury pool design.
How a Backyard Infinity Pool Works, Step by Step
The vanishing edge depends on a constant loop of moving water. Three parts make that loop possible.
The weir wall
The weir wall is the edge itself. It is built a fraction of an inch below the pool’s water line, and the top has to be dead level along its entire length. Water spills over this wall in a thin, even sheet. If the wall is off by even a little, the sheet looks uneven, and the illusion falls apart.
The catch basin
Below the weir wall sits a hidden trough called the catch basin, or surge tank. It collects every bit of water that pours over the edge. The basin is usually formed from the same concrete structure as the pool and tucked out of sight beneath the edge. It also has to hold the extra water that gets displaced when people climb in.
The recirculation pump
A separate pump pulls water out of the catch basin, sends it through filtration, and returns it to the main pool. That keeps the pool topped up so water keeps flowing over the weir wall. The result is a closed loop. The same water cycles over the edge and back again, so none of it goes to waste.
The Engineering Details That Make or Break It
A vanishing edge leaves little room for error. Small mistakes show up right away, either in how the water looks or in how the structure holds up over time. These are the details that matter most:
- Level tolerance. That dead-level weir wall has to stay within a fraction of an inch across its whole length, which is why infinity pools are almost always built from concrete rather than pre-made shells. It also makes the construction process more demanding than a standard pool.
- Surge capacity. Sizing the catch basin is its own calculation. AQUA Magazine, a pool industry publication, points to water-in-transit, bather surcharge, and the effects of wind as the factors that decide how large it needs to be. Get it wrong and the basin overflows or runs dry.
- Structure. The edge wall and basin face far more water pressure than the other sides of the pool. That section needs heavier reinforcement and a footing designed for the extra load.
- Soil and slope. Since many of these pools sit on hillsides, the ground has to be stable enough to hold the structure without shifting. Settling at the edge can ruin the level line, the whole effect of which depends on.
- Waterproofing. The weir wall is wet on both sides, so sealing it well keeps water from migrating through and causing damage later.
Getting all of this right comes down to the team doing the work, so choosing an experienced builder matters more here than on almost any other type of pool.
Energy and Upkeep
A backyard infinity pool runs a second pump that a standard pool does not, so it uses more energy. The answer is to size that pump well and run it efficiently.
Upkeep is a little different too. The catch basin acts like one long skimmer running the length of the edge, so it needs regular cleaning to keep working well.
Many builders also run tile farther down inside the basin, because the water level there rises and falls and plain plaster does not hold up to that back and forth.
Is Your Yard Right for an Infinity Pool?
If your backyard drops toward a view, you already have the one thing a vanishing edge needs most. The rest comes down to engineering it correctly.
Wells Pools can walk your site, model the edge in 3D, and tell you honestly what the slope and soil will allow before you commit to anything. To find out what is possible on your lot, request a free quote or call (916) 638-8810.