Can you drink harvested rain?
As the Philippines braces for a potentially strong El Niño, rainwater harvesting is gaining attention as an alternative water source, as even President Ferdinand Marcos Jr. called on Filipinos to ready their buckets.
A Filipino chemical engineer, however, cautions that collected rainwater isn’t necessarily safe to drink without proper treatment and lab testing.
Eleanor Olegario, founder and chief executive officer of Lithos Manufacturing, said rainwater can pick up microorganisms, animal waste, airborne pollutants, and chemical contaminants as it falls through the atmosphere and comes into contact with rooftops, gutters, and storage containers.
“Clear and clean water is not necessarily safe to drink,” Olegario told the DAILY TRIBUNE, stressing the need to distinguish water suitable for general household use from water that meets drinking water standards.
Bird droppings, animal urine and decaying leaves can contaminate rainwater collected from rooftops. Poorly maintained storage facilities can add contaminants, making the water potentially unsafe for human consumption even when it looks clear.
Olegario said filtration can remove certain impurities, but a system’s effectiveness depends on the contaminants it is designed to address. Her company’s mineral-based filtration system, for instance, can capture some bacteria but does not eliminate all of them and is not a fully validated microbial disinfection system.
Tech-infused
The system uses nano-modified natural zeolite, calcium carbonate, activated carbon and fine-particle filters to help reduce certain chemical contaminants, improve water quality and remove suspended particles. However, these filtration stages alone do not establish that the collected water is potable.
“For us in the scientific community, credibility means distinguishing between what technology can already provide and what still requires validation,” Olegario said.
She said rainwater could potentially be made suitable for drinking through additional treatment, including properly designed ultrafiltration, chlorination and ultraviolet sterilization. Laboratory testing would still be necessary to verify the treated water’s safety.
Under Philippine drinking water standards, water intended for human consumption must undergo testing for microbiological, physical and chemical parameters, along with other applicable requirements. Passing water through a filter cannot rule out harmful microorganisms or chemical contaminants.
Chemical contamination also warrants further investigation. Olegario called for studies to determine whether rainwater collected in different parts of the Philippines contains per- and polyfluoroalkyl substances (PFAS), commonly known as “forever chemicals.”
These substances have drawn international concern because they persist in the environment. Olegario identified industrial activities, agricultural practices, textile production and hospital waste effluents as potential areas for investigation.
She cited Metro Manila as a possible research focus. Still, she emphasized that actual testing, not inferences from potential pollution sources, must establish the presence and concentration of PFAS in Philippine rainwater.