"We are heading toward an ecological catastrophe," said Shaddad al-Atili, water and ecological affairs advisor to the Palestinian Authority, citing Gaza's rapidly growing population.

Some 1.3 million people, 900,000 of them refugees, currently live in Gaza.

It has one of the world's highest population densities, with 3,457 people per square kilometre (8,642 people per square mile), and the population is expected to climb to 2.2 million people in 10 years, according to official statistics.

UN environmental experts are expected in Gaza next week to evaluate damage to the territory's water system, caused by pollution in the water table as well as poor drainage, decontamination and purification facilities.

The team is also to investigate the possible presence of industrial pollutants in the water table and the burying of solid waste at Israeli settlements that were evacuated in August.

Palestinian water expert Said Abu Jalala said another area of focus will be the impact of sand mining by Israeli companies.

"Tens of thousands of tons of high-quality sand have been taken out of Gaza by the Israelis for their industrial glass and building needs, thereby depriving the water table of its natural filter," Jalala said.

In addition, water reserves are low, experts say.

Atili said natural rainwater alone is not enough to sustain the Palestinian territory, which receives between 45 and 55 million cubic metres (1.5 billion to 1.9 billion cubic feet) of rainwater per year but consumes about three times that amount.

"Water is scarce in Gaza and its only water table on the coast is in the process of draining," he said.

"Besides, Israel has not authorised us to import water from regions outside Gaza," Atili added.

Israel has offered to sell them desalinated water for one dollar per cubic metre, which the Palestinians find too costly.

Water allocation is part of late-stage negotiations between Israel and the Palestinians over the creation of an independent Palestinian state, along with other sticky points such as border-drawing, the status of Jerusalem and the return of refugees.

Scarce water has caused Gaza residents to dig unauthorised wells.

Some 4,300 wells are allowed by law, but another 2,400 have been dug without permission, illegally draining 70 million cubic metres (2.4 billion cubic feet) from the already low water table, Atili said.

The extra drainage has the effect of making the drinking water saltier.

In some regions, the salt level reached 300 milligrams per litre, or 12 times higher than international standards of 25 milligrams.

In other regions, the salt level tops 400 milligrams per litre, said Atili, who added that pollution is also a major problem.

"Some 30 million cubic metres of water is polluted each year by fertiliser and industrial by-products that infiltrate the water table due to the decontamination facilities or because of their poor conditions," said Atili.

In a bid to reduce the strain on Gaza's water supply, the US Agency for International Development (USAID) has planned to install a desalination center for sea water that would have an initial annual capacity of 22 million cubic metres (770 million cubic feet) and could reach 55 million cubic metresbillion cubic feet) by 2018.

However, the project has been held up by security concerns and the Palestinian uprising, or intifida, which began in 2000.

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