Angat Dam, which supplies most of Metro Manila’s potable water, could hit the critical level tomorrow and authorities have already ordered limits to use as an irrigation source.
The state weather bureau said the reservoir’s water level fell to 180.73 metres early yesterday, near the key mark of 180 metres, which is expected to soon be breached given an average daily decline of 0.40 metres.
Angat, whose normal high water level is 210 metres, could see this further drop to 173.5 metres next month based on dry season and El Nino rainfall forecasts plus projected water usage, the Philippine Atmospheric, Geophysical and Astronomical Services Administration (Pagasa) said.
Located outside the metropolis in the province of Bulacan, Angat Dam supplies 90% of Metro Manila’s water needs. Its lowest recorded level is 157.56 metres, posted in July 2010 when the country was also experiencing an El Nino.
The continued water level drop prompted the National Water Resources Board (NWRB) yesterday to order reduced irrigation water allocations.
“Considering the current level of the dam, the board has decided to approve an allocation at least for the month of May,” NWRB Executive Director Sevill David said in a news briefing.
While water releases for the Metropolitan Waterworks and Sewerage System (MWSS) will be maintained at 48 
cubic metres per second (cms), the allocation for irrigation will be reduced to 10cms, substantially lower compared to 40cms and 35cms in March and April, respectively.
This would have “no significant impact” on farmers since crops were nearly ready for harvest, David said.
“Because they are nearly ready to do their harvesting, they normally require less water,” he said.
While Metro Manila supplies will not be affected, the NWRB urged residents to conserve at least 4 litres of water or a total of 48mn litres daily to reduce demand on Angat Dam.
Elsewhere in Luzon, other dams are also experiencing declining water levels to the lack of rainfall.
Authorities identified these as Ambuklao Dam in Benguet at 740.16 metres (down 0.08 metres), San Roque Dam in Pangasinan at 251.67 metres (-1.07 metres),
Pantabangan Dam in Nueva Ecija at 195.27 metres (-0.18 metres), and Caliraya Dam in Laguna at 286.25 metres (-0.44 metres). All are still within normal levels.
Some reservoirs, on the other hand, are posting increasing levels: Binga Dam at 566.50 metres (+0.41metres) and Magat Dam at 172.91 metres (+0.06 metres), as these have received sufficient amounts of rainfall.