Manila Water Company: Water Supply System

Water Supply System

Raw Water Sources

The Angat-Ipo-La Mesa Dam Raw Water System is currently the major source of water for Metro Manila. The water abstracted from it is treated in two facilities- The Balara Treatment Plant (Manila Water Company, Inc.) and La Mesa Treatment Plant (Maynilad Water Services Inc.).

Angat Dam

The Angat Reservoir and Dam are located at the Angat River in San Lorenzo, Norzagaray, Bulacan. The facilities were constructed from 1964 to 1967 and have been operational since 1968. They have multi-purpose functions:

To provide irrigation to about 31,000 hectares of land in 20 municipalities and towns in Pampanga and Bulacan;
To supply the domestic and industrial water requirements of residents in Metro Manila;
To generate hydroelectric power to feed the Luzon Grid; and
To reduce flooding to downstream towns and villages.

Image of Angat Dam The principal river, Angat River, originates from the western flank of the Sierra Madre Mountains. It then cuts through the mountainous terrain in a westerly direction to the dam site. The elevation within the watershed rises to a maximum of 1,115 meters at the Sierra Madre Mountain range and is lowest at the dam site at 100 meters. It has three major tributaries, namely, the Talaguio, Catmon and Matulid Rivers. The Angat Watershed has a moderate to intensive forest cover and has a drainage area of about 568 square kilometers, which receives an average annual rainfall of about 4,200 millimeters.

The Angat Dam is a rockfill dam with a spillway equipped with three gates at a spilling level of 219 meters. Its storage capacity is about 850 million cubic meters. Water supply to the MWSS is released through five auxiliary turbines where it is diverted to the two tunnels going to the Ipo Dam.

Ipo Dam

Image of Ipo Dam The Ipo Dam is a gravity concrete dam located about 7.5 kilometers downstream of the Angat Dam near its confluence with the Ipo River in Bulacan. It was completed in January 1984 with a maximum storage capacity of 7.5 million cubic meters, an increase of about 2,500 million liters per day (MLD) from the old Ipo Dam, which used to be located 200 meters upstream of the new dam.

The spill level of the dam is at an elevation of 101 meters and it has seven radial floodgates. The watershed topography is characterized by mountainous terrain similar to the Angat Reservoir Watershed with moderate forest cover. The watershed has an area of about 70 square kilometers and receives an average annual rainfall of 3,500 millimeters. Tributaries to the Angat River at this section include the Ipo, Sapa Pako and Sapa Anginon Rivers. These tributaries drain into the Angat River from the eastern section of the watershed.

Water from the dam is diverted to the Novaliches Portal and the La Mesa Dam through three intake structures going down to three connecting tunnels into five connecting aqueducts.

La Mesa Dam

Image of La Mesa Dam The La Mesa Dam is an earth dam located in Novaliches, Quezon City. It was first erected in 1929 and then further raised in 1959 to a maximum storage capacity of 50.5 million cubic meters. Overflow level of the dam is at an elevation of 80.15 meters. The watershed has an area of 27 square kilometers, which receives an average annual rainfall of 2,000 millimeters.

How water is transmitted

From the Angat Dam, water flows through two concrete diversion tunnels down to the Ipo Dam. The Ipo Dam serves as an intermediate intake and water is then conveyed through three intake structures at the dam going to three connecting tunnels. Both Tunnels 1 and 2 have a length of 6,400 meters each and have a capacity of 760 MLD and 1,890 MLD, respectively. Tunnel 3 is about 6,100 meters long and has a capacity of 2,000 MLD.

Water from the three tunnels flows to three settling basins in Bicti, Norzagaray which are then connected to five Bicti-Novaliches aqueducts. Aqueduct Nos. 1, 2, 3 and 5 are each about 15 kilometers long while Aqueduct No. 4 is about 1,650 meters long and each comprises multiple segments of pipe siphon and tunnel. Aqueducts 1 and 2 share common tunnel segments interconnected with parallel dual pipe siphons and have a combined capacity of 380 MLD. Part of the flow at Basin 1 is diverted to Aqueduct No. 3 that has a capacity of 830 MLD. Aqueduct Nos. 4 and 5 have a capacity of 1,250 MLD and 2,000 MLD, respectively. The five aqueducts can deliver a maximum capacity of 4,500 MLD at the Novaliches Portal.

At the Novaliches Portal most of the water is conveyed through three open channels going to La Mesa Treatment Plants 1 and 2 and the Balara Treatment Plant. The rest of the water goes directly to the La Mesa Dam. The La Mesa Dam has three intake structures, with three connecting aqueducts to the Balara Treatment Plant ranging from 7,500 and 6,700 meters long. Both Aqueduct Nos. 1 and 2 have the same capacity of 565 MLD while Aqueduct No. 3 has a capacity of 1,140 MLD.

Aqueduct No. 3 is joined by the 1,700 meter Balara Bypass that is connected at the Novaliches Portal and has the same capacity as the said aqueduct. From Aqueduct No. 3, water flows to Balara Treatment Plant No. 2 while the water from Aqueduct No. 1 goes to Balara Treatment Plant No. 1. Water from Aqueduct No. 2 is diverted either to Balara Treatment Plant No. 1 or 2. Another bypass located at the interconnecting line between the Balara Bypass and Aqueduct No. 3 is connected to Aqueduct No. 1. This bypass is operated when the La Mesa level falls below 71 meters to divert the water directly to the Balara Treatment Plant instead of to the dam to prevent further water losses at the dam due to seepage and evaporation.

At the Alat River near Novaliches, a low weir with flashboards on the ogee crest diverts stream flows through an aqueduct going to the La Mesa Dam. This aqueduct is about 2,000 meters long and has a capacity of 380 MLD.

The Treatment Process

Image of Water Treatment Plant Water Treatment in Balara consists of four processes, namely, coagulation/flocculation, sedimentation, filtration and disinfection. In the coagulation/flocculation processes, coagulants and coagulant aids are mixed uniformly with water to be treated to allow bridging or adhesion of individual particles into flocs that settle more easily. This is accomplished by a slow, extended mixing process that converts minute particles into discrete, suspended particles. Balara Treatment Plant No. 1 has 12 vertical-type, motor-driven flocculators per basin while Balara Treatment Plant No. 2 has nine flocculators per basin. Detention time is 20 minutes. Balara Treatment Plant No. 2 has 12 basins, each of which has a capacity of 120 MLD. Balara Treatment Plant No. 1, meanwhile, has two basins with a capacity of 140 MLD per basin. Determination of coagulant/coagulant aid dosage to be adopted for plant use is obtained by conducting a jar test. The flocs are then made to settle down in the sedimentation basin and this is accomplished by enlarging the area of the basin to reduce the velocity of the water and adopting a chemical dosage which has a greater settling rate than the designed overflow rate of the basin. Detention time is about two hours. After the sedimentation process, water to be treated is passed through a media consisting of several layers of graded sand and anthracite to screen out all foreign particles which did not settle down in the sedimentation basin. Detention time is around 20 minutes. The Balara Treatment Plant uses the chlorination method of disinfecting water. Chlorine is applied at three points: pre, intermediate and post-chlorination. Pre-chlorination is applied for taste and odor removal and is usually 0.3 mgl. Intermediate chlorination is for filter aid while post-chlorination is for disinfection purposes, having dosages of 0.3 and 1.2 mgl, respectively. Finally, water is then sent to distribution by gravity and by pumping.

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