By Severino C. Samonte

La Mesa Dam and Metro Manila's water supply system

January 12, 2023, 12:59 pm

Most of the over 13 million residents of the 16 cities and one town of the National Capital Region (NCR) may be interested to know that the La Mesa Dam in the former town of Novaliches is the oldest among the three dams consisting of the Angat-Ipo-La Mesa water system that provides potable water to the Metropolitan Manila area and nearby provinces.

Novaliches, a municipality that existed from 1855 to 1903, is now divided between the neighboring Quezon City and Caloocan City.

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 the 1920s, 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) Prof. 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.

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

During the early years of the American regime, the Wawa Dam was the first source of water supply for the people of Manila and its 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.

Novaliches, then still under the 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. according to the MWSS website, construction of the 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 or Hilltop, Norzagaray, started in 1961 and was completed in 1967, also during the second year of the first Marcos term (1966-1969).

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 the Angat and Ipo dams in Bulacan, automatically becomes the barometer of the 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.

The rainy season also places La Mesa Dam in the national news 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.


About the Columnist

Image of Severino C. Samonte

He began his journalistic career by contributing to the Liwayway and Bulaklak magazines in the 1960’s. He was the night editor of the Philippine News Service when Martial Law was declared in September 1972. When the Philippine News Agency was organized in March 1973, he was named national news editor because of his news wire service experience.

He retired as executive news editor in 2003. He also served as executive editor of the Malacanang-based Presidential News Desk from 1993 to 1996 and from 2005 to 2008.