BANGKOK (Thomson Reuters Foundation) - Bangkok’s tap water supply may run out in a month, as the country waits for long overdue rains to replenish sources depleted by drought and threatened by seawater creep, the chief of the capital’s water authority said.

The skyline of central Bangkok and the Chao Phraya river are seen during sunrise in Bangkok April 22, 2015. REUTERS/Athit Perawongmetha

Thailand is suffering its worst drought in more than a decade. In an effort to maintain water levels in the dams that supply water for agriculture in the provinces as well as taps in the capital Bangkok, the government has asked farmers to refrain from planting rice since last October.

Despite these measures, water levels are critically low in the three key reservoirs that flow into the Chao Phraya River, one of the two main sources of Bangkok’s tap water.

The quantity of water collected in the three dams totaled 5 billion cubic meters last November, compared to the normal 8 billion cubic meters, said Thanasak Watanathana, governor of the Metropolitan Waterworks Authority. As of Monday, there was about 660 million cubic meters left, according to the Royal Irrigation Department.

“Right now, there is only enough water in the dams to distribute for about 30 more days – if it doesn’t rain,” Thanasak told the Thomson Reuters Foundation in an interview.

Normally, the flow of water from the rains and dams keeps saltwater from the Gulf of Thailand at bay. But during droughts, the saltwater creeps upstream, turning the Chao Phraya brackish.

The seawater can kill crops and threatens the pumping station that siphons off water from the river, about 100 km (60 miles) from the gulf. The waterworks authority produces 5.2 million cubic meters of tap water per day for 2.2 million residential, business and industrial customers, but is not equipped to treat saltwater.

“Some days the saltwater increases, we don’t intake the water from the Chao Phraya River. We stop and use the water from the Metropolitan Waterworks Authority stocks of water in canals. We can stop intake for 3 hours,” Thanasak said.

The waterworks authority has asked Bangkok residents to store a reserve of 60 liters of drinking water in the event of a shortage. It has also urged people to use less water, but has had little success on this front in part, said Thanasak, because water customers pay only 8.50 baht ($0.25) per 1,000 liters.

“It’s too cheap, so people don’t feel the need to conserve. It has been this price since July 1999. It’s probably the big city with the cheapest water in the world,” he said.

The Metropolitan Waterworks Authority plans to invest 45 billion baht ($1.3 billion) over the next seven years to increase production and storage. It has also started discussions on a 30-year plan to forecast water demand, identify sources of water and protect against saltwater intrusion, Thanasak said.

Large-scale rainwater collection should be part of that solution, he said, adding that currently when it rains in Bangkok, all the water drains into the sea, wasted.

“We also have floods every year, and we waste that water by letting it out to the sea. So how can we save some of that water to solve the problems during the dry season?” he said.

“They are releasing so much rainwater into the sea. It’s more than we have in our entire dam system. Even if we could save 10 percent of it, it would be a lot.”