Of all Vegas’ pool parties—Wet Republic at MGM Grand (billed as Vegas’ first ultra pool), the Palms’ Ditch Fridays, Tao Beach’s Sunset Sundays, Venus at Caesars, Bare at the Mirage … if I missed your favorite, no disrespect—I’ve only been to one: the spring break-ish peo-pool-alooza that is Rehab at Hard Rock.

I was amazed by the crowd, a few thousand, I’m guessing, more people than I’d see at some Rebel football games. (Just kidding.) Also amazing was how pool-goers, having already parted with up to $40 to get in, happily forked over more cash for food and drinks.

That pool parties are big business is obvious—look at the iterations the Hard Rock has begat—but just how big is anyone’s guess. MGM Mirage spokesman Alan Feldman couldn’t quantify how pool events impact, er, bottom lines at Mirage or MGM Grand.

Christina Canseco, an associate account executive for Preferred Public Relations, says pool parties contribute to Tao Las Vegas’ success. “Tao Las Vegas was the highest-grossing restaurant in America last year, grossing $66.6 million. This was an 11 percent increase, year over year, and Tao Beach played a big role in this. The pool has seven luxury cabanas with Xboxes and plasma screens. We have no problems selling those out.”

On weekends, nearly 1,300 guests go to Tao Beach. Rehab draws crowds more than twice that—3,000 on average. Though she declined to cite specific numbers, Hard Rock spokeswoman Dorian Cantrell says Rehab’s revenues are 40 percent over 2007. Using admission figures—$30 for women, $40 for men—it’s safe to assume the Sunday party brings in at least $90,000, excluding what’s spent on food, shopping and gambling.

Another barometer of how important pools are to major resorts can be seen in enforcement. Some numbers:

Eleven: Number of Southern Nevada Health District inspectors assigned to inspect pools in major resorts.

Yearly: Frequency of pool inspections

$320: Fee for closing a pool due to environmental concerns. “It’s not a lot of money,” says Gregg Wears, environmental health supervisor for the Strip’s Las Vegas office.

Four: In feet, the separation state law requires between food and a pool.

Zero: Amount of glass allowed near a pool.

Daily: Frequency resort pools are cleaned out. Wears says most resorts have dedicated staff whose sole responsibility is maintaining the pools. They do everything from cleaning furniture to sanitizing the water to power-blasting—using high-pressurized hoses to clear surfaces around the pool.

During their random checks, health district inspectors check out safety equipment and gauge the water’s chemistry—examining alkalinity and pH levels, among other things.

On rare occasions, they respond to customer complaints.

“We might be at Rehab and look at how things are going,” Wears says. “If there’s something wrong, it behooves the pool operator to fix it. The fine is inconvenient because they have to go the office and pay the fee. They also have to put up a sign that says the pool is closed and explain to their guests why they can’t use the pool.”