Once upon a time, city kids envied suburban kids and their backyard swimming pools. But now, urban kids of all ages can be cool in the pool, too at the rooftop watering hole.

This high-dive trend has big-city developers crowning downtown hotels, and condo and apartment complexes, with pools. As land becomes more precious, and pricey, experts say the rooftop pool will become even more commonplace.

?Where there?s a higher density of people, you start to see elevated pools because of cost of land and value of the land,? said Doug Whiteaker, principal at Water Technology Inc. in Beaver Dam, Wis.

Examples range from The Berkeley in London, where A-list celebrities flock to the hotel?s rooftop waters, to The Hotel in Miami designed by Todd Oldham, to the Colonnade in Boston (Boston?s only rooftop pool, also known as RTP), to the Pegasus Apartments in Los Angeles.

In fact, many say the craze was jump-started in downtown L.A. In 2002, the Standard Hotel opened, and its rooftop pool and bar quickly became a hot spot. Developers have been trying to outdo each other with sky-high aquascapes ever since.

?Owners and developers are willing to spend more money on elevated pools and to spend money in their design and finish for that reason,? said Carol Anderson, architect at Counsilman-Hunsaker in St. Louis.

The allure of these aquascapes is their spectacular views and the ability to create communities in an urban setting. Many of the rooftop settings include lush gardens, cafes and/or bars, which naturally attract residents and guests.

Pools also tend to be decidedly high-end because of their significant sales function in condos and developments, Anderson said. For example, some pools cantilever off edges of buildings with glazed ends, or use infinity edges. ?We see things like ? waterfeatures integrated into comprehensive architectural designs with much greater care than would often be found comparable to in-grade civic design,? she said.

Such pools are not without construction challenges, though. Engineers must factor in the thousands of pounds of water that a building?s columns need to support. That might mean a shallower pool, or placement on a platform to better distribute the weight and contain any splash- out. Designers also have to be wary of what?s beneath the pool, to avoid leaking onto a nice space such as the ballroom.

Along with special attention to waterproofing, deck draining and piping, designs are limited in terms of spray features and vanishing edges. Even something as simple as a service elevator that can safely transport chemicals must be considered.

To ensure lighter vessels, designers lean toward stainless steel or fiberglass. Then there?s the issue of how to get pool components to the roof. It?s usually done by crane or airlifted via helicopter.

No wonder construction of these sky-high facilities can be nearly triple the cost of their ground-floor cousins, according to Whiteaker. But he adds that after construction, the outdoor rooftop pool is a lot less expensive to operate than indoor facilities.

In the end, the guests and owners win. ?It?s a nice amenity people enjoy, whether they?re going to get in the water for wellness or social benefit,? Whiteaker said. ?[Developers] have gone from putting them in enclosed areas on intermediate floors to taking them to rooftops opening them up with great views, to have the outdoor experience.?