From early morning, housewives carrying buckets and brass pots queue in the back streets of Nepal's capital for the free water pumped from a network of ancient stone spouts.

A lifeline in a city with erratic government supplies and expensive private alternatives, Kathmandu's intricately carved communal spouts have survived invasions and earthquakes.

But the centuries-old water taps are now suffering from a much more modern threat, the rapid development of the chaotic capital, to the despair of thousands of Kathmandu's residents who depend on them.

"We don't have the luxury of buying water for everyday use... I don't know what I will do if this stone spout dries up," mother-of-three Namita Maharjan, 34, said as she waited to collect water near her home.

The population of sprawling Kathmandu has expanded by 60 percent in a decade, according to Nepal's 2011 census, with some 2.5 million people requiring 350 million litres of water per day.

But the struggling city's government is only able to meet about half that demand and private companies charge up to $11 for 1000 litres (264 gallons) -- an unaffordable price for many residents -- making the free taps a critical part of Kathmandu's infrastructure.

For Maharjan, whose husband earns just $150-200 a month, the threat of losing her neighbourhood spout -- which she describes as a "blessing" -- is terrifying.

Already more than half of the valley's 389 spouts have fallen into disrepair, according to a 2006 survey by the Kathmandu-based NGO, Forum for Urban Water and Sanitation (NGOFUWS).

More are expected to dry up as unregulated construction blocks underground water channels, which has prompted some residents to dig their own tube wells indiscriminately.

Hotels, construction firms and private industries are also digging their own wells, which has caused an alarming dip in the groundwater table. Between 1995 and 2013, levels fell by an average of 2.5 metres (98 inches) per year, according to government figures.

"Unplanned urbanisation and over-extraction of groundwater is crushing the ancient supply system of the spouts," says NGOFUWS secretary Anil Sthapit.

- Religious ritual -

The spouts dotted throughout Kathmandu date back to the sixth century when the city, now a traffic-clogged concrete jungle, was home to hundreds of temples.

A prince belonging to the Licchavi dynasty built the taps, known as "dhunge dhara" in Nepali, in a bid to provide clean drinking water to citizens.

The spouts, adorned with carvings of Hindu and Buddhist deities, were often built near the myriad of temples, and continue to play a key role in religious rituals today.

"Water from the spouts is considered very pure... daily rituals in many temples begin with an offering of water to the gods," says Sandhya Khanal, who is currently pursuing a PhD focused on the history of the stone taps.

"Despite this, they are allowed to disappear."

Once the heart of the neighbourhood, where women gathered to gossip, the last tap built in Kathmandu, the gold-plated Sundhara, or "golden spout", was cherished by the poor.

But it began to run dry in 2003 soon after builders dug the foundations for one of Kathmandu's first malls, blocking the underground channels that fed the tap.

"Low-income communities depend most on the spouts because the water is free. When the tap dries up, it directly affects the poor," NGOFUWS campaigner Sthapit told AFP.

"The rich have alternatives, the poor don't."

- No alternatives -

NGOFUWS is attempting to raise groundwater levels and revive worn-out taps by promoting rainwater harvesting and running public awareness programmes to keep the spouts clean.

But Sthapit said the government has done little to preserve the still functioning ones.

"We are doing what we can, but enforcing building construction rules so that underground canals aren't destroyed...is beyond our jurisdiction," he said.

In the past, communal governing bodies called "guthis" supervised maintenance of the spouts, but most are no long active today, leaving the government in charge.

The government itself has placed the blame back on residents, while bemoaning its own lack of resources.

"Stone spouts are important cultural sites that need to be conserved," said Shriju Pradhan, chief of the government's heritage division.

"The local community is not pro-active in protecting the spouts...and unfortunately we don't have enough resources or the expertise to conserve them," Pradhan told AFP.

Housewives Shanti Nakarmi and Pramila Lama have little sympathy, as they fret over their local spout on the fringes of the city's iconic Durbar Square, which is offering less and less water each month.

"We sweep the courtyard occasionally and try to keep it clean. What more can we do...(when) we don't know where the water source or channels are," Nakarmi told AFP.

Lama added: "If the government cannot give us water, the least it can do is save what our ancestors left us."