Rain is stored in what is called a watershed. When rain falls, it collects in the undergrowth of the forest. The undergrowth of a forest is the shrubs, herbs, dead leaves and roots on the forest floor. The undergrowth acts like a sponge. When it is full, the accumulated water begins to drip into the ground and down into what are called aquifers or underground rivers that feed our creeks, streams and rivers.

And, believe it or not, there is one in Metro Manila. The water that runs through your pipes and keeps millions of Metro Manilan’s quenched and bathed, keeps industries running and farms producing comes from only one source - the La Mesa Watershed and Reservoir.

The 2,700-hectare watershed occupies some areas of Quezon City, Caloocan and Montalban, Rizal. A watershed is land that drains the water it collects into a body of water, like the reservoir, which is an artificial lake where water is collected. The La Mesa Reservoir filters 1.5 million liters of water to Metro Manila. That’s a lot of water.

Presently, 1,200 hectares of the La Mesa Watershed is denuded or without trees. This means that no undergrowth exists and therefore, just like in the cities, most the water from rain has no place to go. Some of it evaporates. More likely, it will run off and carry precious soil down to the river, as there are no more roots to hold the soil. This is called erosion. And it doesn’t end here. When soil is carried down to the river, silt is formed. This not only kills the plants and creatures that live in the river, but also causes it to overflow and flood nearby communities. Floods are therefore not caused by uncollected garbage. Garbage only makes it worst.