The practicality of ‘harvesting’ rainwater

MANILA, Philippines - The rains are here, so why not “harvest” them.

Rainwater is a beautiful “resource from the heavens,” and harnessing them for various uses can considerably help boost the national economy, particularly the agriculture sector.

Studies so far conducted show that agriculture is the world’s largest water user, consuming about 70 percent of the total global supply.

A Philippine Rice Research Institute (PhilRice) report, for instance, says, “Asia receives 22 percent of the world’s population, which means that competition for water is very high.”

Rainwater is not only of vital importance to agriculture — it also has other domestic uses such as watering plants, flushing the toilets, and even as drinking water.

Rainwater harvesting technology has been practical since the ancient times, according to studies.

PhilRice, the Department of Agriculture’s research arm, says, “The technique usually found in Asia and Africa arose from practices employed by ancient civilization within these regions and still serves as a major source of drinking water supply in rural areas.”

What is water harvesting?

It is, according to Dr. Cecilia Gascon, president of the Southern Luzon State University, “a system that collects rainwater from where it falls than allowing it to drain away… It is the collection and storage and also other activities aimed at harvesting surface and groundwater, prevention of losses through evaporation and seepage and hydrological studies and engineering inventions, aimed at conservation and efficient utilization of the limited water endowment of physiographic unit such as watershed.”

In the Philippines, particularly in the farming sector, rainwater harvesting has been practical in rural communities through the small farm reservoir (SFR) or small water-impounding project (SWIP).

SFRs have become fixtures in some Central Luzon villages, notably Sta. Catalina where these have been the subject of studies. A number of these SFRs have also been supported by government funding institutions.

Some SFRs have also been doubling as fishponds, thus augmenting their owners’ income. Moreover, they serve as a “swimming pool” in summer.

Records show that more scientific rainwater harvesting started in the country in 1989 with the assistance of the International Development Research Center (IDRC) of Canada.

About 500 tanks made of wire-framed ferrocement with capacities varying from two to 10 cubic meters were constructed.

“Income-generating activities in Capiz (Panay Island) prompted the implementation of (rainwater harvesting) in the Philippines,” reports PhilRice.

Under the system, a participant was lent $220 payable in three years. The amount covered the tank and income-generating activities such as swine-raising and other livelihood projects.

This way, according to PhilRice, direct subsidies are avoided, unlike in the case of financing rural water supplies.

Rainwater harvesting also offers other advantages. For instance, it reduces the rate of power consumption for pumping of groundwater, according to Gascon. “For every one-meter rise in water level, there is a saving of 0.4 kwh of electricity,” Gascon says.

In coastal or saline areas, rainwater provides good quality water and when recharged to groundwater, it reduces salinity and helps in maintaining balance between the fresh-saline water interfaces.

On islands, owing to limited extent of freshwater aquifers, rainwater harvesting is the most preferred source of water for domestic use, according to another study.