MANILA -- Did you know how La Mesa Dam in Novaliches, a former town now divided between Quezon City and Caloocan City, became part of the Angat-Ipo-La Mesa water system which supplies potable water to residents of the present Metropolitan Manila and nearby provinces?

According to the book “Ang Kasaysayan ng Novaliches” (History of Novaliches) published in 1997, La Mesa Dam, located about 20 kilometers northeast of Manila, was constructed in 1929, or during the American occupation of the Philippines.

The book, written by historians Dr. Emmanuel Franco Calairo and his mother, former University of the Philippines-Los Baños (UPLB) professor Rosalina Morales Franco-Calairo, narrated that between 1920 and 1926, the former Metropolitan Water District (MWD) decided to build a new dam to replace the old Wawa Dam in the town of Montalban (now Rodriguez) in Rizal.

Then MWD was the predecessor of the former National Waterworks and Sewerage Administration (NWSA), now the Metropolitan Waterworks and Sewerage System or MWSS.

During the American regime, the Wawa Dam was the first source of water supply for the people of Manila and environs, which used to be a province itself prior to the creation of the present Rizal province in 1901. Owing to Manila’s fast-growing population, this source of water supply became obsolete and needed to be replaced.

The former town of Novaliches, then still under full jurisdiction of Caloocan municipality, was chosen by the government as the site of the new dam because of the sloping topography of the Novaliches watershed from the neighboring Bulacan province, notably the towns of Norzagaray and San Jose del Monte, now a city.

Meanwhile, as La Mesa Dam turns 90 years old this year, it becomes the oldest among the three dams comprising the Angat-Ipo-La Mesa water system.

According to the MWSS website, construction of Ipo Dam in Barangay San Mateo, Norzagaray, Bulacan began in 1935.

It was partially opened in 1936 and improved to its present condition during the administration of former President Ferdinand E. Marcos in 1984.

On the other hand, construction of the Angat Dam in Barangay San Lorenzo (Hilltop), Norzagaray, started in 1961 and was completed in 1967.

The La Mesa watershed, located in Barangay Greater Lagro, Novaliches, is under the joint administration, supervision and control of the Department of Environment and Natural Resources (DENR) and the MWSS.

The La Mesa reservoir, which has a capacity of up to 50.5 million cubic meters, attains full capacity during the rainy and typhoon seasons.

Once its water level reaches the maximum of 80.15 meters, the water spills to the nearby Tullahan River which passes through North Caloocan City, Valenzuela City, Malabon City, and Navotas City before emptying into the vast Manila Bay.

Today, whenever the summer or dry season is around, La Mesa Dam frequently lands in the national news — whether print or broadcast.

This is because the dam’s water level, along with that of Angat and Ipo dams in Bulacan, automatically becomes the barometer of water supply available for the people being served by the Maynilad Water Services Inc. and Manila Water.

When La Mesa Dam’s water level falls to the critical mark of below 69 meters, it is a signal for the MWSS, Maynilad, and Manila Water to regulate water supply to their customers.

On the other hand, the rainy season also places La Mesa Dam in the national news.

This is because when the dam’s water level reaches its maximum level of over 80 meters, particularly during heavy rains and strong storms or typhoons, the excess water overflows to the downstream Tullahan River, threatening residents along low-lying shores of the waterway.

This, in turn, prompts authorities to issue periodic warnings to said residents to be on constant alert for possible floods in their areas. (PNA)