KARACHI: Mohammad Ramzan pumps water into a large goat skin bag before carrying it down an alley and up several flights of stairs to deliver to a resident in Karachi, Pakistan's largest city.

For more than four decades Ramzan has been a "mashki", or water bearer, an age-old profession now in decline as water companies and tankers increasingly supply residents.

But his services are at least in high demand during the Islamic holy month of Ramadan, during which fasting can be a challenge when the weather is hot.

"In Ramadan, the poor mashkis have a very tough time delivering water to us inside buildings that are four or five storeys high," said resident Mohammad Imran, as Ramzan, 60, arrived with his load.

"The tanker people often do not even answer our calls; they also charge too much. We are really grateful to these mashkis."

Karachi needs about 1,200 million gallons per day of water to meet the demand of its estimated population of 20 million people. But officials say its two main water sources only provide the city with about 580 million gallons per day.

Some of the water is lost due to dilapidated infrastructure and water theft, while experts say climate change and dams built upstream by India also reduce water supplies.

Ramzan stops to catch his breath as he climbs the narrow stairwell, carrying his leather "mashk" which can normally hold up to 35 litres of water.

"During the month of Ramadan, it becomes especially difficult for people to collect water from water points, so I bring water for them in the hope that Allah will bless me for it ... I also earn my living this way."

Water bearers have existed in South Asia for centuries, providing water to travellers and warriors during battles in ancient times.

But Ramzan worries that the days of the mashki are numbered.

"Tankers are delivering water everywhere; mineral water companies are supplying water from house to house," he said.

"Because of this, the profession of the mashki looks like it will not last long."