MODESTO, Calif. — With school out and hot weather in full swelter — er, make that swing — it's that time of year: swimming pool season.

Homeowners with backyard pools are dusting off the lounge chairs, unpacking float toys and stocking up on chlorine and other supplies as they prepare to get their swim on.

A quick survey of the kinds of in-ground swimming pools people are installing at their homes shows how much pool design and construction have changed in 30 years.

Back then, residential swimming pools typically were rectangular or kidney-shaped holes in the ground. The pool bottom was white or light-blue plaster and the pool itself was surrounded by concrete.

Fast forward to 2007.

Today's custom pool buyer can pick from a number of options, styles and designs.

Want a pool that looks like an oasis plucked from nature?

Done.

How about one with a built-in rock waterfall that sounds like a babbling brook?

No problem.

Or, how about a pool that's attached to an outdoor kitchen bar and has underwater seats, so swimmers can literally belly up to the bar for a beverage or snack without having to get out of the water?

Yep, that, too, is possible.

Those are just some of the options that pool construction companies such as Aqua Pool & Spa in Manteca, Calif., offer.

Pool design preferences, just like architecture and clothing, come and go depending on consumer tastes, according to Aqua Pool's Gregg Whitley.

"In the 1980s and early '90s, formal design was more popular than natural lagoon-style pools," Whitley said. "Somewhere in the mid-1990s, an overwhelming reaction to the lagoon concept really prevailed in design for about a 10-year run."

Today, people building a pool from the ground up are just as likely to select a formal Greco-Roman pool as a natural-style pool. Regardless of the style, an increase in the availability of exotic materials and features at prices more people can afford are helping pool owners customize their pools.

Historically, homeowners adding pools to their property were families and empty-nesters with grandchildren.

But in the past five to six years, said Whitley, "there's been a lot more interest from those who do not have kids but who just want that architectural element within their home and yard that a pool offers."

How much one spends on pool construction depends on factors such as the design, materials and extra options, including water features and lighting.

The cost to build a standard pool starts at about $24,000. Add an in-ground spa and the price increases to $30,000 or $40,000.

Add custom finish (such as Pebble Tec), lighting, a couple of water features, an attached outdoor kitchen and a high-end hardscape such as slate, granite or travertine and the price can soar as high as $500,000.

"People are trying to create an inviting serenity in their yard," Whitley said.

Because it is such a costly investment, shoppers need to make sure the company they hire is reputable and properly licensed.

Some suggestions:

• Make sure any contractor you're considering is licensed and in good standing.

• Get three references and review their work.

• Get at least three bids.

• Get a written contract and do not sign anything until you understand all terms.

• Pay only 2 percent or $200 down — whichever is less — for swimming pool projects. Do not let payments get ahead of the work.

• Do not make a final payment until completion of the final plastering, decking or equipment installation.

• Do not pay cash.

• Keep a file of all paperwork related to the project.

Here are some examples of current trends in pool design:Shallow pools becoming standardIn the 1970s and '80s, swimming pools had maximum depth of 8 to 9Z\x feet. Today, more people are requesting pools with a maximum depth of 5½ to 6½ feet. Shallow pools are more affordable because it costs less to build, heat and maintain them.<B>Expanded finish choices</B>Remember when the bottom of the pool was merely light-colored plaster? Now, buyers can select custom finishes such as Pebble Tec, which gives the pool bottom and water a richer, deeper color. Depending on the selected finish, it can make the pool water appear as dark blue as a late-evening sky or an ocean aqua.<B>Water features</B>Pool owners are adding water features — fountains, scuppers, descents — that are visually interesting and audibly soothing. Waterfalls can be incorporated into the pool's design, either by way of a retaining wall or pergola, or they can stand alone. You can program some water features to function with pool lighting for more dramatic effect.<B>Expanded hardscape choices</B>Pools of yesteryear typically were surrounded by concrete. Today, pool owners can select tile, slate or a textured surface.<B>Vanishing-edge pools gaining popularity</B>This high-end option, which is also referred to as a negative edge or infinity edge, is designed to look as if the pool extends all the way to the horizon and does not have any edges. This option is pricey and can add as much as $15,000 to pool construction costs. It requires more space, too.<B>Integrated landscaping</B>Pool owners and builders no longer are leaving landscaping as an afterthought. Designs now incorporate places where flowers and trees can be added to enhance the pool area's overall look.