England is no place for the thrill-seeking hydrophile. True, this summer the whole country became one giant water park, but minus the slides and fun. So when we heard that Europe's largest water park was opening this week in sunny Tenerife, my partner and I booked the next flight out.

It's the perfect place. Not only is Tenerife a constant 22-24C (71-75F) year round, with little rain, but the place also screams adventure. It surges from the ocean like the mysterious island of Dr Moreau, or King Kong, or Lost, its volcanic mountains rising to almost 4,000m (13,000ft). Raquel Welch was filmed in her shrinking fur bikini on its basalt moonscape; Nelson lost his arm to a cannon while trying to wrest it from Spanish hands.

So how does Siam Park, so-called for its Thai theming, measure up? First impressions were spectacular. The owners of Tenerife's long-established animal sanctuary Loro Parque have gone beyond building a mere collection of water slides and pools, and created a bona fide theme park.

Lengthy technical delays - the park was due to open earlier this year - have allowed the vegetation to flourish: 8,500 palm trees have been planted on the previously barren hillside, irrigated by the same desalinated sea water that is used on the slides to avoid depleting the island's precious reservoirs. And the main rides are fronted by awesome sculptures: a giant Thai warrior, a 30m-high temple and the world's largest dragon.

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I was itching to try the slides and in my determination to be the first journalist down the terrifying Tower of Power, I found myself with a whole theme park pretty much to myself. It was just me, my partner of 25 years (our envious kids having been left to their schooling), the rides' effervescent American designer, a few of the owner's friends and family - and 75 underemployed lifeguards.

You could bottle the fun we had and sell it as an elixir of youth. The overstressed mother of our teenaged children screamed like a schoolgirl as the Dragon ride tilted us into a near-vertical drop, the sudden acceleration propelling us 5m up the curved wall of a giant funnel, then down and up the other side, and so on until we were expelled giggling and gasping into the lowest pool.

The Volcano whisked us round and round what the makers would probably like to call a giant whirlpool, but was more like being flushed down a Brobdingnagian toilet.

There were many other rides, including the world's longest Lazy River to relax on, a whole Lost City for under-10s, and a long white beach overlooking a surf school on 3m-high artificial waves. But the pièce de résistance, clearly, is the Tower of Power. The only ride you do bareback, ie without using an inflatable tube, it drops you 28m down a near-vertical slide, then cannons you through an enclosed pipe in a tank filled with alligators.

According to Siam Park's director, there is only one other ride quite like it, in Nassau, and that is 10m shorter. It is, quite frankly, absolutely bloody terrifying. My partner refused point-blank to do it. Just watching me climb the steps turned her knees to jelly and her face white.

The view from the top is magnificent. You drink in the bright blue sky and sheer volcanic peaks as though they were your final sight on earth. You are told to lie down, cross your ankles and fold your hands over your chest. It makes you feel as though you were already dead and being prepared for embalming. Certain in the knowledge that no one can survive such a drop, you relinquish all pain and earthly struggle. And then, with a helpful shove from the lifeguard...

Actually, I have little memory of the split-second before I emerged at the bottom blind, coughing and with water having been forcibly sluiced through every orifice. But alive! I felt like a million dollars. And the next time, with eyes wide open and nose held shut, I could even enjoy the ride.

I've been to several of the great American water parks - Schlitterbahn, Six Flags, Disney - and in many respects Siam Park tops them all. Lord knows what it will be like if it becomes as successful as it deserves to be. The stone paths can get painfully hot for sensitive soles, and there is no shade for long queues. But for now, it's quite simply the most fun you can have with your clothes off.

NEED TO KNOW

EasyJet (www.easyjet.com) flies to Tenerife from Gatwick, with prices from £66.98.

Siam Park is in South Tenerife, just off highway TF1, exit 28. Nearest bus station is Playa de las Americas. Tickets £22 adults, £14 children (www.siampark.net/en).

The Gran Hotel Bahia del Duque (00 349 22746900, www.bahia-duque.com) has double rooms for £299 B&B.

More information Spanish Tourist Office (020-7486 8077, www.spain.info/uk); Tenerife Tourist Board (www.webtenerife.com)

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