Some of Phuket's tranquil lagoons began life as abandoned tin-mining craters. When the miners finally laid down their equipment, they left areas of the island scarred by a toxic acne of rainwater pits. Then something delightful happened. The land was reclaimed by major resort operations, marinas, golf course and even bungy-jumping facilities. Today, people come from around the world to admire jungle-fringed ponds and lagoons while relaxing at five-star resorts and spas, little dreaming that some of this lovely scenery lies atop a once-ravaged earth.

Many of these former mining sites have been cleaned up and transformed into valuable natural and commercial resources. Today, however, a different potential for disaster lurks — something that could turn Phuket into a parched island thirsty for fresh water. Ever hear that line about "Water, water everywhere but nary a drop to drink?"

Phuket being an island, says Bradley E. Kenny, president and senior environmental engineer of Thailand-based Environmental Solutions and Protection Corp Ltd., seawater intrusion is always going to be a concern. Lots of Phuket residents and businesses dig wells to extract fresh water, which suggests another enduring wisdom: "Nature abhors a vacuum." In this case, it means that salt water will find ways to leak into wells near the coast where fresh water has been removed. Where that happens enough with a sufficient number of coastal wells, Phuket's water table could be opened to flooding by the Andaman Sea.

"The prime local example," says Kenny, "is Phi Phi Island. Five or six years ago, the deep wells on Phi Phi Island produced the same quality of water that we now get here on Phuket. But because of all the resorts that were built, and because it's a smaller island, now there isn't one single deep well on Phi Phi Island that doesn't suffer from salt-water intrusion. The wells now on Phi Phi Island are up to 2,000 to 3,000 parts per million salt, which makes the water unusable."

Nor is this relentless invasion by the sea Phuket's only drinking problem. Bacteria — single-celled micro-organisms that can wax parasitical if they like you enough — are responsible for much of the world's disease. Much like the tourists who flock to Phuket to enjoy the warm, relaxed ambience, lots of bacteria, especially keen on microscopic watersports, also love Phuket.

"The biggest problem with Phuket's drinking water is bacteriological," Kenny says, "and that's mostly the result of improperly installed or non-functioning septic-tank systems or small home waste-water systems. Bacteria could be leaking from the septic tank into the ground, which then gets into other groundwater sources — shallow or deep wells alike — and it could be leaking into rivers or streams and polluting some of the lakes and reservoirs. There probably are cases of mild dysentery and things like that that could be attributed to this problem."

Don't freak if you're in Phuket Town or Patong Beach, because those zones have municipal waste-water systems. More good news: Phuket doesn't have much industry, and thus does not suffer from major industrial pollution. The bad news is all those abandoned tin mines sitting out there like ghostly black holes. Lakes that filled the pits are now soaking gunk-infested sediment from the mining process. Scoop up some lake water, and you might find higher concentrations of aluminium and, in some places, arsenic than international standards allow for drinking water. "The tin mining has been so long gone — 70 or 80 years ago —- that I believe most of the arsenic has settled down," says Kenny. "But I believe research into the bottoms of these lakes would reveal elevated arsenic levels".

A more immediate threat appears to be aluminium, which has been linked to Alzheimer's disease. Aluminium is naturally abundant on Phuket. It now threatens underground wells, pipes and sediment. More recently, nitrates have infiltrated Phuket's water supply, often from over-fertilizing golf courses and rubber plantations. Nitrates can especially target kids, entering their blood streams and, in some cases, causing blue-baby syndrome, in which an infant can turn blue because nitrates rob the bloodstream of oxygen.

Don't despair, however, because most of Phuket's drinking water is just fine. Kenny emphasizes that, in general, because of the lack of industry, water quality on Phuket is surprisingly good. To protect future supplies, however, the "tin-mine lakes" will need special care. If you're looking for something to do on your holiday to combine scenic views, relaxation and a bit of ecology, take a look at the inland lagoons along Bang Tao Bay, and you'll see what some water experts hail as the wave of Phuket's future. Some of the most luxurious resorts lined up along Bang Tao Beach offer their guests the joys of inland lagoons. Or, as the five resorts which comprise Laguna Phuket like to boast in their brochure: "The resorts are linked by sparkling lagoons." Charming Thai-style boats shuttle guests across blue water that offers a "lagoon-side function venue," "lagoon dining" and rooms with a "lagoon view" along "the placid water of dreamy lagoons".

The whole Laguna Phuket area was once a tin-mining area," says Kenny, "and that's an extraordinary environmental story — how they transformed it. Basically, that land was environmentally condemned. Then Laguna's developers bought and reconditioned it, and now it's some of the most successful property on the island." Engineers dredged the pond bottoms, brought in topsoil and reconditioned the land. They saw that the biggest problem wasn't contamination, but rather the loss of topsoil as a result of the mining. The extent to which Laguna's clean-up efforts succeeded is astonishing.

Actually, according to some water-table surveys, plenty of fresh water lies under Phuket. Those reservoirs already in place can, if necessary, be extended and multiplied with fresh construction. "But the amount of bacteria we see on Phuket is more than what I would consider normal," warns Kenny, "due to improperly installed waste-water treatment systems. So you can get water out of the ground — not much problem there — but you then have to make sure it doesn't get polluted by bacteria on the way to your drinking glass. If you live on a hill, for example, the water in your well probably comes from higher up. If rubber plantation workers dwell there, their septic tank may be rudimentary. To freshen the water, you can chlorinate it, de-chlorinate it, and then pour it through a "reverse-osmosis" system that acts like a molecular-level sieve to block bacteria and other micro-organisms.

You can also pray to the rain gods, because Phuket is almost solely dependent on rainfall. In any case, Phuket probably won't suffer too many water woes until the year 2010. Then it may be crunch time, if the population continues to expand at the current rate.

Amid all the talk of salty water, bacteria and contaminants, the subject of future water for sale is already making some investors drool. "There are lots of privately-owned old tin mines from which people sell water," Kenny says, turning glum. "And it's usually untreated water. Most of the resorts that are buying it, fortunately, have their own treatment systems."

Only a lucky portion of this island — mostly Phuket Town and Patong — is part of any municipal water system, where consumers can turn on a tap and pay the piper. For future fluid in areas where there is no tap water, the hope is to rehabilitate more former tin-mine lakes, and then truck water to where it's needed. But tanker trucks have limited capacity. Kenny, who sells desalination systems, insists that salt-removal is much better than trucking: "It's cost efficient. Components would come from overseas, sure, but the final assembly and manufacturing would be right here. The desalination membranes are almost all manufactured in the US, but the pressure vessels are already made in Thailand. All the electronics, all the controls, the frame, everything, would be locally made. When people hear about de-salination, they don't know about the advances that have been made in technology within the past three or four years. They imagine huge plants that take lots of manpower and skills to operate, and believe that it must be expensive. But this just isn't true. Technology in desalination has moved forward in many ways, just as it has in IT."

Last year, global warming, the El Nino weather system, booming tourism and other changes all conspired to put undue pressure on supplies. The 2002 dry season reduced the 8.5-million-tonne capacity of Phuket's main tank to a mere 2.11 million tonnes of water. To wring more from the island, Phuket officials reportedly dredged two more tin-mine lagoons to boost Phuket Town's supply, also arranging to feed a couple more lagoons into the main Bang Wad Reservoir.

"Patong is the only place where we have announced that tap water is safe to drink," Dr Jessada Chaikunrat, deputy chief of Phuket's Provincial Public Health Office, was recently quoted as saying, "because the distance from treatment to point of consumption is short, so the water is less likely to be contaminated before it comes out of the tap. We have not yet declared water in other places safe to drink because we are not sure."