In 1947, inventors Carl Hauber and Robert J. Koupal, of Delaware-based Infilco Inc., filed a patent for a precast concrete swimming pool that is “compact and cheap in construction” with a built-in recirculation system.

And get this: Their design didn't include main drains.

Instead of “extraneous piping” conducting water to a remote filter, this concept houses all the plumbing within the structure. This includes the pump and filter, which are contained in a well at “one end portion of the basin” and accessible from above through a manhole and ladder. The advantages of this approach are many, the inventors note. Because the recirculation system is contained within the basin, this eliminates stress on pipes that is caused by “unequal settling of the ground.” But the main benefit Hauber and Koupal tout is hydraulic efficiency.

Their recirculation system is gravity-fed, drawing water from the surface through a “plurality of ports in the wall … which are equally spaced around the basin at the predetermined level.” These connect to a conduit that slopes slightly from the shallow end toward the pump well, positioned at the deep end. This conduit could also double as a splash gutter and is the only channel through which water is fed to the filter. The main drains serve no circulatory function other than to remove water to waste, and would be equipped with “suitable plugs.”

This method, they argue, allows for a more uniform withdrawal of water from the upper layers, where much of the scum and contaminants reside.

Dan Johnson, owner of Swim, Inc., in Sarasota, Fla. thinks the system has merit. “Conceptually, I love the idea,” said Johnson. It’s similar to how he constructs pools. In 2002, he developed the Swim-Safe System, which pulls water from the surface and distributes filtered water evenly throughout — no main drain required. “In terms of efficiency … that is far and away the best way to circulate a swimming pool.”

However, there is a flaw in Hauber and Koupal’s plan. While their gravity-fed design emphasizes uniform withdrawal, the way it brings water back into the basin isn’t ideal. There is only one return fitting and it’s at the deep end. Even at a high velocity, “by the time that water randomly finds its way to the other end of the pool, the efficacy of sanitation and heat distribution is going to be radically diminished,” Johnson said. “That’s the one shortcoming of this system.”

While their idea of a precast concrete pool poses logistical concerns — Johnson cringes at the thought of craning a massive concrete shell above a building — Hauber and Koupal’s notion of a surface-only recirculation system was on the right track.

Today, motivated in part by VGB requirements, a small number of builders have embraced the drainless approach. Even San Juan Pools, a fiberglass manufacturer, decided in 2015 to make pools sans drains.

It seems Hauber and Koupal were ahead of their time.