Sex and chlorine are in the air, making the hot tub (or more technically, the spa) the undisputed star of Realityland.

Millionaire bachelors and giggly bachelorettes strip down and hop into them almost constantly, as if by network fiat, on the nation's most-watched television shows. By turns horny, happy and awkward, the hot tub is our agreed-upon surrogate of intimacy, and what's intriguing is how normal it seems: If you believe in the reality seen on reality TV, then the whole world hinges on Jacuzzi moments.

Why the hot tub?

"The hot tub is a really good excuse to get good-looking people into bathing suits," says Mike Darnell, the Fox network executive who is considered a pioneer in the outer limits of reality programming. "I also think there is a genuine relationship between young romance and the Jacuzzi. No question. . . . The Jacuzzi is to this generation what the drive-in movie was in the '50s."

There are about 5 million in-ground whirlpool spas in America, according to the National Spa and Pool Institute, but to casually channel surf, you'd swear there were even more. Hot tubs everywhere! Filled with muscle-bound lunkheads and boob-augmented ditzes about to be "Elimidated" or denied the precious long-stemmed rose of survival; hot tubs occupied by conniving, fornicating housemates who live in over-decorated cribs, each about to vote the other off into teleblivion.

A bubbly soak in the big spa is a sacramental baptism of impending humiliation -- whether on higher-budget network shows like "Joe Millionaire," "Meet My Folks" and "The Bachelorette," or in the lowly land of syndicated dating games. In the hot tub's pH-balanced bacterial stew, almost every semi-manufactured plotline comes to a frothy head: Hold on, Trista's getting in the La Quinta hotel hot tub now with some of her bachelors! Viewership steams up in anticipation, as the hot tub scene gets us closer to a potential transaction of flesh.

But that's just part of it.

There's also something delicious about the atmosphere of tackiness in which all of this occurs. On Monday's episode of "Joe Millionaire," paramour Evan and his date for the evening experienced hot tub interruptus when three more competing babes decided to join them for a dip. Footsie ensued.

The women set up for letdown on "Joe Millionaire" (Evan is, viewers are told, earning $19,000 a year) haven't stopped to think that a real millionaire would never sit around in a hot tub. Not like this. Not on a date.

The hot-tub assignation is strictly the realm of thousandaires, wannabes and people seeking to rekindle a fossilized marriage. Or ski bums, or mooks from the shore.

In these hot tubs one can sense a defining conflict of taste, of class. Realityland adheres to such tropes as the single red rose and mid-price champagne; it believes in the candelabrum and horse-drawn carriage rides through parks; it believes that there's something wonderful (and not at all junior-senior prom) about riding in stretch limousines.

In fact, everything television knows about love and seduction it seems to have learned from a 15-year-old girl. (Wait. That's insulting to 15-year-old girls. Everything television knows about love it learned from the husband who forgot Valentine's Day and is trying to make up for it.)

And everything TV knows about sex, apparently, requires a hot tub.

The hot tub occupies the psychic space formerly reserved, in more chaste eras, for the cutaway shot to the fireplace. It goes back as far as "Love, American Style," the late '60s, when certain Californians were pioneering the plumbing and kinky aesthetics needed for an outdoor group bubble bath.

No longer confined to honeymoon suites and the backyard deck of the "interesting" neighbors, the ubiquity of the 21st-century luv tub -- indeed, it's a fixture now in suburban master bathrooms -- proffers more evidence of a culture split lurking just beneath the surface: A significant part of the national lifestyle gets a little more inelegant all the time, even as it seeks elegance. It's not a moral failing so much as an inexorable loss of discernment.

Hot-Tub Nation: Every day in America, another woman considers buying a session of boudoir photography. Every day in that America, a young man is enticed into the magic muscle powders sold in his local strip mall's GNC. Somewhere out there, people are still buying water beds, and accessorizing with red satin sheets, or booking "romantic" cruises on ships where they are likely to acquire some viral gastric distress. Somewhere out there (Los Angeles, actually) women are taking lessons in pole dancing from strippers, who promote its cardiovascular merits.

All in the name of an elusive thing called "sexy."

Deferring to the eye of the beholder, let us behold the hot tub: How can something so restful, therapeutic and really not much different from a kiddie pool go from being a mundane experience to a preamble to copulation? Are hot tubs sexy? Is sex in a hot tub all that great? (We answer definitively: "Eh.")

Witness poor Warren Schmidt, the recently widowed, newly retired and certainly baffled character played by Jack Nicholson in the current movie "About Schmidt." Late in the story, he has an unnerving encounter in the backyard hot tub belonging to a Rubenesque, New Age hellion named Roberta Hertzel (Kathy Bates). Roberta is the queen of Too Much Information, disrobing for a full-frontal moment that rivals anything on television for reality. "I think it was a really strong benchmark visual," Nicholson told the Chicago Sun-Times of Bates's saggy creepiness. "That shot is about the reality of life."

Naturally -- all too naturally -- Roberta comes on to Warren while they're in the hot tub. His horror is the horror of anyone who ever felt unwanted footsies in the suds.

In the (real) real world, hot tubs are unexotic, sort of gross, vaguely tempting. When you check into a Hampton Inn, on business, it's the first thing you smell -- that trapped, indoor chlorine mixed with the leftover aroma of the free continental breakfast.

Consumers buy hot tubs for two reasons, according to National Spa and Pool Institute survey data. "First is stress reduction, and I can attest to that," says spokeswoman Suzanne Barrows. "The number two reason is family togetherness. The spa has replaced the dinner table."

But then there's that other world: The producers of MTV's "The Real World" and "Road Rules" are perhaps the hot tub's greatest adherents. Over time they have learned to stock the house with a pool table, booze, condoms and a hot tub large enough to accommodate the entire cast. Three of last season's Las Vegas housemates got overly acquainted early on in the tub, as if it had cast some spell on them. Later the Southern girl fretted on camera that her daddy was going to see the show and think she was a slut.

The hot tub is always so still and cold and unbubbly the morning after.

But oh, for a few minutes in Joe Millionaire's Jacuzzi. There's a bleachy moral cleansing behind all that steam: "Nothing happened in the hot tub," more than one vixen or stud has assured her or his reality-cam inquisitor. (Usually it is hidden cameras -- in that distinctive convenience-store robbery graininess -- that provide audiences the hot tub scenes they really long for.) "Something almost happened in the hot tub," says a man trapped in "The Real World." And still another of Realityland's witless participants wipes a guilty tear from her face and confesses: "I feel bad about what happened in the hot tub."

Yet this is the exact kind of thing that transfixes viewers: The knowledge that anyone would get in a hot tub with high hopes in the first place. You lose your mind in the hot tub. Soon enough you're wet and bloated and the color of a canned Vienna sausage. Your makeup is running. The bachelor is playing footsie with you, while simultaneously building you up for a fall.

Nothing good can happen in the hot tub.

Which is precisely why there's always one handy.

Staff writer Lisa de Moraes contributed to this report.

On "The Bachelorette," Trista and a few of her remaining choices schmooze in the tub.Decadent dunking on the NBC reality show "Meet My Folks": A delicious, bubbly stew of tackiness. In Fox's "Joe Millionaire," last one into the hot tub apparently is a rotten egg.