How British golfers and tourists are turning Spain and Portugal into dust

British expatriates in Spain are helping to exacerbate Spain's worst drought for more than half a century. The demand for golf courses, swimming pools and luxury homes is part of a growing crisis over the country's rapidly dwindling water supplies.

Nearly two million foreigners, mostly Britons, now own Spanish coastal holiday homes, and some 350,000 new homes were built on the southern coast alone last year.

Iberia's traditionally parched southern flank is showing signs of turning into desert. It's not just that Spain and Portugal are gasping for water in their worst drought for more than half a century. Nor that the region's numerous reservoirs are down to 20 per cent of capacity in many cases, or that desperate farmers are demanding record sums to compensate for ruined crops and livelihoods.

This is not just another bad year, when the authorities reduce the pressure of domestic tap water and turn off beachside showers - although both these things are happening. "This is the beginning of a long cycle of drought," Spain's Environment Minister, Cristina Narbona, said recently. The really worrying thing is that the structural shortage of water that has afflicted the southern half of Spain and Portugal since the Arab occupation more than a millennium ago cannot today be palliated by ancient irrigation skills, modern desalination efforts, more reservoirs or the diversion of rivers from the watery north.

"Even without drought, our rivers carry less water than they did 20 years ago," Ms Narbona warned. Scientists fear up to a third of Spain may become desert in 50 years. Global warming is partly to blame. But so too is the frenzy of luxury property development that sucks up ever more precious water in a part of Europe that has never had enough.

Spain has built 160 golf courses since 2000, overwhelmingly in the south, and 150 more are planned, to meet insatiable demand from affluent visitors from northern Europe, keen to play under sunny skies. Spain's golf business turns over more than €2bn (£1.35bn) a year - a figure that has nearly tripled since 1997. When you land at Alicante airport, hoardings beam captivating images of sparkling greens stretching to the blue horizon, with appeals in English to buy into the latest luxury development. Drive south through Murcia to the coastal towns of Aguilas and Mazarron and you cross terrain that could be Arizona, gashed by bulldozers, dotted by gleaming new houses.

British residents here are proud to show off their luxury homes, but are vague about whether the water that fills their private pool and gushes from their showers is piped from distant rivers or drawn from fast-depleting ancient aquifers. It certainly doesn't fall from the sky. Murcia is technically desert, whose bald rock and badlands resemble North Africa rather than Europe. Rain comes twice or three times a year, and then mostly runs to waste over scrubby soil.

How do these verdant fairways retain their spongy brilliance? "The majority of owners of these golf courses don't tell the truth," says Julia Martinez, a specialist in water resources at Murcia University. "The water authorities have been turning a blind eye for decades, despite knowing that courses rarely use recycled water, which they are supposed to do. Furthermore they often buy water from farmers who have a well, which is illegal. In a situation of chronic scarcity like that of Murcia, where water is more important than petroleum, the proliferation of golf courses is unsustainable."

The golf greens form only part of the picture. The influx of thirsty residents with their shopping malls, bars, restaurants and clubs may bring prosperity to a poor region - as developers claim - but they dramatically intensify demand on reserves. "Thousands of new wells have been dug illegally in Murcia, and resources are being exhausted," says Ms Martinez. "Demand for water is unstoppable: every drop supplied creates the demand for two more. Ancient springs are drying up, and water is becoming contaminated with salts and nitrates. Wells plunge 600 metres, the water table is falling and aquifers are saying basta - enough."

Things are even worse in Portugal, where serious drought afflicts some 70 per cent of the country, especially the traditionally parched southern Alentejo region, now also a favourite spot for upmarket tourist developments. "These are very, very difficult times," said Francisco Palma, head of the Alentejo Farmers' Association. "Things have never been this bad." Portugal recently asked its neighbour for €6m compensation because of a 50 per cent fall in water from the river Douro, which rises in Spain.

When Spain's Socialists came to power last year they scrapped a €4.3bn plan to pipe water from the Ebro to the parched south. The cost, and environmental arguments against the brutal disruption of an extensive river system, proved overwhelming. Worse, the plan pitted the watery regions of Aragon and Catalonia against their parched southern neighbours

Perhaps more than a third of water is lost by leaky pipes. Big savings could be made just by investment in maintenance. Farmers - the biggest water consumers -are reluctant to abandon traditions of flooding their fields, in favour of drip irrigation using recycled water. But even if these lapses were corrected, campaigners say the delicately balanced ecosystem of Spain's southern coast has been so violated by overdevelopment that it faces destruction. "The reality is that we are consuming twice as much water as our rivers and aquifers can provide," says Julia Martinez.

"We must make new plans. Our system of intensive tourism and inefficient farming is simply unsustainable."