Few things in the backyard will inspire the instant awe of a well-done perimeter-overflow pool. They cast an ethereal air over just about any space.

The vessel essentially overflows and spills across the bond beam. Deck and water merge into one so the pool appears to be a large mirror. As a side benefit, these pools can make a yard look larger since there is no coping or raised bond beam to interrupt your gaze.

But these installations aren't for every homeowner. “A perimeter-overflow pool is not particularly family-friendly,” says Steve Sargent, president of Elite Custom Pools in Lake Forest, Calif. “Kids doing cannonballs are going to create a lot of splashout.” This can leave the deck slippery and create a hazard for children.

Perimeter-overflow technology is complicated and requires a high level of technical expertise along with an acute eye for detail. Below is a primer outlining the main challenges of these installations. However, no single article can teach anyone to build a perimeter-overflow pool. It's important to take a class or consult with an experienced professional before attempting this type of project.

How they work. The basic workings of a perimeter-overflow pool are deceptively simple. It's essentially a vanishing edge around the entire pool. Water fills the vessel until it overflows and spills into a receptacle, generally an underground gutter that runs around the pool. In some systems, the gutters are large enough for storage, but in most cases they direct water to a remote holding tank.

Most perimeter-overflow pools sit flush with the deck. This version is also referred to as a rim-flow, slot-overflow, or wet edge. After spilling over the top of the pool, the water enters the gutter through a grate or a ¼- to 1-inch slot. The latter is becoming more popular as many consider grates less attractive. However, some manufacturers now offer grates in stone.

Another type of perimeter-overflow installation sits above the ground and looks more like an overflowing bowl. While rarely used for pools, this option is becoming increasingly popular for spas. Water falls over a raised wall and into a surrounding moat-like catch basin, or a slot system for the wet-deck effect. Designing access into the pool or spa can be tricky, because you have to interrupt the flow with a set of steps leading up the wall.

Breaking it down. There are five concerns when it comes to engineering and constructing perimeter-overflow pools:

The Edge. The edge refers to the weir where water breaks from the surface and falls into a gutter or catch basin. In that regard, a rim-flow pool is like a vanishing edge times four, since water has to sheet over the entire perimeter.

Those concerned with energy efficiency will want to overflow the pool using the least amount of water possible, which allows you to power the system with a smaller pump. However, it also results in a thinner film wetting the edge. If aiming for this effect, you need the entire perimeter to be as close to perfectly level as possible. Otherwise, water will take the path of least resistance, spilling in a thicker sheet over lower parts of the pool and leaving higher spots dry. Pool builders recommend working with a ¼-inch “tolerance” at most. This means the entire perimeter must fall within ¼ inch of level. Most experts shoot for closer to a 1/16- or even 1/32-inch tolerance.