The La Nga River, part of the Dong Nai River, has been narrowed due to salinity and water shortages. Climate change could also shorten water supplies for HCM City residents this year. Photo Ngoc Ha

City residents could face a water shortage this year as El Nino and climate change caused an unexpected increase in the salinity of the Sai Gon and Dong Nai rivers, which provide most of the city's water.

The salinity rate in the rivers is the highest in the last five years, which has affected the operations of some of the pumping stations that supply water to the city's nearly 10 million population.

The Sai Gon Water Corporation (Sawaco) has reported that in January and this month, Binh An, a Malaysian joint-venture water treatment plant with a capacity of 100,000cu.m a day, had to cease operations for several hours a day on several days due to excessive salinity in the Dong Nai.

The maximum permitted salinity rate is 250mg per litre.

The Hoa Phu pumping station in Cu Chi District has also had to shut down, especially on high-tide days, when more seawater flows upstream.

It is expected to stop operating for four to six hours a day in the coming period. During the worst periods, the company has to use water stored at other treatment plants to sustain supply, Bui Thanh Giang, the company's general director, said.

A study by the company found that the salt content in the Sai Gon was 358mg per litre last month and 340mg in February compared to 0.9mg in early 2012.

Giang said the rate is likely to be much higher in the coming months since the dry season has just begun.

Shortage

To deal with the imminent water shortage, the company has drawn up co-ordination plans under which if one or more treatment plants have to suspend operations due to salinity, others, even those it does not own, will operate at full capacity to make up the shortfall.

There are almost 10 plants in the city, some of which are owned by the company, though it is the sole distributor and the other plants sell water to it.

The company has built storage tanks for treated water with a combined capacity of 100,000cu.m in some of its treatment plants, and they would be put to use soon, Giang said, assuring that with these measures there would be no water shortage at this time.

But he admitted the situation over the next few months is unclear since the rainy season would only start in June.

For years the company has been getting the Dau Tieng-Phuoc Hoa reservoir in Tay Ninh and the Tri An hyower plant in Dong Nai to release water in case of high salinity in the rivers.

But unfortunately, the water level in the former is much lower than in previous years, and the reservoir's capability to release water is low. The level is at 22.46 meters, 2.15 meters lower than in mid-November.

Don't panic!

Rik Dierx, resident project manager of the Dutch-funded project "Climate Change and Water Supply in the Mekong Delta and HCM City" called on the city not to panic and to instead do something about the situation.

He suggested that the city should build a raw water reservoir that can hold at least a day's supply of river water so that when the salinity rate is high, the treatment plants do not have to draw water directly from the river and can continue normal operations.

At the Sawaco's main river water pumping stations the salinity rate is high during high tide and much lower during low tide, he said.

"If you have a day's storage capacity, you can draw water at low tide and can stop the intake when the salinity is high. However, if you do that, you would not need to cease the water treatment processing."

In this way, HCM City can secure public water supply for an estimated two decades, or even more, but without the raw water reservoir, the salinity problem would rear its head earlier, he warned.

"With the current salinity situation, we do not yet have a problem that is out of control and cannot be properly managed by Sawaco. It is not yet that urgent, but we can make our future situation safer by building the reservoir."

There are ideas to take water directly from Dau Tieng and Tri An reservoirs, but it would be very costly. Building relatively small reservoirs &ndash a day's supply only &ndash would be much cheaper, allowing us to delay the implementation of expensive investments for many years, he said, but added that one should not stop planning for the long term solutions.

The Netherlands has built reservoirs, he explained, initially prompted by intrusion of seawater affecting public water supply in the port city of Rotterdam, but designed to address many other water quality issues.

Giang said that Sawaco supports the idea of building a reservoir, and has submitted plans to the city government.

Depending on the size of the land that is provided, the scale of the reservoir would be decided though it can be expanded later, he said.

Giang too said there are plans to draw water from the Dau Tieng Reservoir after 2020.

Besides, the company has started studying reverse osmosis technology for use when the salinity situation worsens.

Sawaco supplies 1.6 million cu.m of water daily to city residents. In January the company treated roughly 50 million cu.m and residents consumed 34 million cu.m.

While the availability of water is decreasing due to climate change and pollution, demand continues to increase relentlessly. In January, for instance, daily demand increased by 105,000cu.m from a year earlier, according to the company