Water at Shatila refugee camp in Beirut’s southern suburbs is now so salty and ridden with chemicals that metal cutlery rusts after less than half an hour’s exposure to the brine.

“Imagine having water so bad that you can’t have metal cutlery? It’s hell water really,” says Ahmed, a resident at the camp.

Gesturing at the salty, foul-smelling liquid oozing from a nearby tap, his friend Moussa Deeb, an electrician originally from Damascus, adds: “Have you ever woken up and tried washing your face with sea water?”

Camp authorities now have to bring in water for bathing and cleaning from outside.

The site of a brutal massacre during the Lebanese civil war, Shatila’s population has doubled to about 40,000 in the four years since the conflict in Syria began. At least 1.5 million refugees are estimated to have spilled over the border into Lebanon, with many seeking affordable housing in the populous coastal strip.

The water infrastructure was already reeling from decades of over-pumping, and the effect of these new arrivals has been devastating.

Families who used to receive four subsidised gallons of clean drinking water a week must now make do with half of that as cash-strapped camp bosses struggle to meet demand. Few communities in Lebanon have seen their water quality deteriorate as dangerously as Shatila, but the camp’s problems point to the country’s difficulties in coping with a sudden 30% growth in population.

“People just don’t realise how critical the status of our water resources is,” said Nadim Farajalla, a professor of hydrology and water resources at the American University of Beirut. “Refugees arriving when there was already a drought really killed us.”

Unlike Jordan and Iraq, both of which have also taken in hundreds of thousands of Syrian refugees, Lebanon usually enjoys a long rainy season and receives ample recharge from melting mountain snows, although rains are beginning to become less predictable because of climate change.

But poor management of water sources and the additional refugee demand have set the country on a destructive path.

“Because of the Syrians, a water balance that should have been negative in 2030 is negative now,” said Fadi Georges Comair, general director of hydraulics and electrical resources at the ministry of energy and water. “We were organised to fulfil water demand management for about 4.5 million [people]. We were not ready to deal with the one-and-a-half to two million extras that have come already.”

Over the mountains from Beirut, and alongside the Syrian border, residents of the agricultural Bekaa Valley are experiencing their own water crisis.

Syrian children attend a class at a school for refugees in the Lebanese village of Qaraoun, in the Bekaa Valley. Photograph: Joseph Eid/AFP/Getty Images

Water demand from the thousands of makeshift refugee tent settlements has meant rivers are drying up earlier than usual. Farmers, who previously resorted to using expensive wells for water in the hot summer months, are now having to pay out for these earlier in the year. According to Farajalla, the effects in a country that already imports 80% of its cereals, and where the amount of land devoted to food has fallen by 45% in 20 years, are obvious. Many farmers have simply given up.

“Every week, there’s a bad pump here or a revolution there, so agriculture is not easy in Lebanon,” said Mohammed al-Arigi, who grows wheat, radishes and a variety of vegetables within earshot of heavy shelling and bombs three miles away across the border.

The crisis has had some compensations, farmers say. The glut of young, desperate men has meant there’s plenty of cheap labour. But the tide of wastewater seeping from the haphazardly built refugee shelters has forced some to shift away from growing vegetables that are usually served raw, such as lettuce, due to concerns about exposure to contaminated water.

Refugees arriving when there was already a drought really killed us Professor Nadim Farajalla, American University of Beirut

Water experts acknowledge that no country of Lebanon’s size could cope easily with such an influx of refugees, but they say infrastructural neglect by Beirut’s paralysed political class has left it particularly poorly placed to handle the crisis.

“Water establishments are highly understaffed, lack financial means, technical competence, and effective internal organisation,” said Marie-Hélène Nassif, a consultant for the International Water Management Institute, who has conducted extensive research in the Bekaa.

A national water strategy proposed in 2010 was never implemented properly due to political disagreements. Authorities are left to practically guess how much water they can count on because they lack the equipment necessary to gauge snowmelt.

Shatila’s residents have tried to offset the terrible water quality by stocking up on rust-proof plastic cutlery. Nearby shops are doing a roaring trade selling water filters that offer the promise of usable tap water.

But civic leaders fear that conditions in the camp, where children are at risk of electrocution by the low-hanging mess of water pipes and electrical wires, will only worsen as more Syrians seek sanctuary among its creaking tower blocks.

“For sure, the population will increase as the Syria war continues,” said Abu Moujahed, director of the camp’s Children and Youth Centre. “And the water and services will, of course, just get worse and worse too.”

• Peter Schwartzstein is a Cairo-based journalist.