MANILA - Metro Manila's principal source of water supply may get depleted in just 3 weeks if rains fail to replenish water in Angat Dam, a scientist said Sunday.

While rains brought on by the southwest monsoon and tropical depression Egay have slowed down the decline in Angat Dam's water level, Dr. Carlos Primo David said the rains were not enough and the reservoir is still way below its critical level.

• Egay stirs monsoon rains; Angat Dam level rises

David, a geologist with the University of the Philippines (UP) Resilience Institute, said the critical level of Angat Dam is 180 meters, but water in the reservoir has already fallen below 160 meters.

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As of 6 a.m., Angat's level was at the 158.64-meter mark, up from Saturday's 157.96-meter level, according to the PAGASA website.

"I calculate that it would increase by about 1 meter after all this rain," David said in an interview with ANC's Dateline.

David, who is a professor at the UP National Institute of Geological Sciences (NIGS), said the recent rains had given Metro Manila an extra 2 days of water supply.

But David added that "we need about 30 days, at least, of that kind of rain that we experienced yesterday" to bring Angat to its normal level.

"We're definitely not out of the woods yet."

At the current supply level and consumption, Metro Manila may have only 3 weeks of water left, David said.

The unused Wawa Dam in Rodriguez, Rizal can be used to augment Metro Manila's water supply while authorities develop a new and bigger water source, he said.

Wawa Dam could be made operational in just 2 to 3 years and supply 100 million liters of water per day. This could be increased to up to 500 million liters per day later, he said.

"That would give us some wiggle room in the next few years until we find a more viable and bigger source."

One source could be the Kaliwa Dam being planned in Infanta, Quezon. But David also noted that this project was still mired in controversies.

ADDRESS WATER DEMAND, TOO

Besides looking for new water sources to increase supply, David said that it was also important for authorities to address the rising demand for water.

David noted that water usage was increasing not just because of the rising number of residents of Metro Manila but also because each resident of the capital was also using more water.

He acknowledged that this was a sign of rising standards of living which would put even more strain on Metro Manila's water supply.

He doubted that supply-side solutions would solve the water crisis if no measure was done to address demand.

"It will always fail if we only look at supply side and not demand side," David said.

He suggested that authorities encourage water conservation measures among households and institutions.

"The money we're paying for water is not really reflective of its value."

The UP Resilience Institute provides information on climate change mitigation and adaptation.