From rooftop to tap: turning rainwater into safe drinking water in the Mekong Delta

In Vietnam’s Mekong Delta, groundwater extraction is driving land subsidence and salt intrusion, while pesticide pollution has made most of the delta’s water sources unfit to drink. With support from Partners for Water, the Nuoc Mua project piloted a rainwater-to-drinking-water system that uses no energy and removes over 98% of pesticides. Inventor and former researcher Albert Jansen (Water Innovation Consulting) explains how this solution originated at a Dutch innovation competition and found its way to four pilot sites in Vietnam.

Jansen developed the technology together with a loose-knit consortium that grew over successive projects: Wageningen University & Research, Your Filter Factory (YFF), Can Tho University, and STEPSVN.

A delta under pressure

The Mekong Delta is one of Southeast Asia’s largest agricultural regions, home to around 20 million people. Decades of groundwater pumping for farming have caused the land to sink, while rising sea levels push salt water further inland. “Farmers risk losing their harvests to salinisation, and their livestock is no longer getting water that’s fit to drink,” says Jansen. On top of that, heavy pesticide use has contaminated most of the water sources in the region. The Vietnamese government wanted a solution, and in 2020 the Dutch embassy in Hanoi launched a prize to find one.

From a citywide vision to a rooftop solution

Jansen’s technology traces back more than a decade to a Dutch innovation challenge, “Stad van de Toekomst” (“City of the Future”), where three ministries invited ideas for sustainable cities. “I first had a very elaborate concept for an entire water self-sufficient city,” Jansen recalls. “But that was far too complex to prove in the eight months allotted.” He scaled the idea down to one detail: turning rainwater into drinking water. “Chemically, rain is a fairly pure resource. It only picks up pollutants from the air, and from the roofs it lands on. That makes it much easier to purify than surface or groundwater.” The concept won the challenge in 2016. Jansen patented it under the name Hemel(s)water – internationally known as Water from Heaven.

No power, no chemicals

The system collects rainwater from clean roofs into a buffer tank, then passes it through a biofilter that removes ammonia, followed by an ultrafiltration membrane. “The membrane is basically a very fine filter,” Jansen explains. “Bacteria and viruses that could make you ill are simply too big to get through.”

Crucially, the process runs entirely on gravity. “It doesn’t use any energy. At most, a small pump is needed occasionally to move the water from the storage tank to the tapping point, and that can run on a small solar panel.” In the Netherlands, the process design is certified by Kiwa to show that it meets official drinking water requirements.

A new challenge: pesticides

Jansen had already piloted the technology in Tanzania, funded by Partners for Water, where published research later confirmed the approach met WHO water quality standards. In the Mekong, however, an additional challenge emerged: pesticides, present in the region’s rainwater at levels far above drinking water standards.

“We bind these pesticides using activated carbon,” Jansen says, referring to the biofilter’s filling. “Even though the standard is strict, the actual quantities involved are tiny. For a large installation, it takes less than one gram of pesticide capture per year.” Results from the pilot show removal rates of around 98.5%, well within drinking water limits.

What isn’t clear yet is whether the pesticides are only bound or also broken down by the biological elements in the filter. “We expect the latter, but it hasn’t been demonstrated yet,” says Jansen. If so, the carbon could stay effective much longer, making maintenance even simpler. Follow-up research should confirm this.

Strong partnerships

Four pilot plants were installed: at a government building, Abavina Company’s greenhouse horticulture farm, a chicken farm, and Can Tho University. Jansen credits much of the project’s smooth running to strong local partners, notably Professor Pham Van Toan and PhD researcher Hoang Hong, both from Can Tho University. Hong also runs his own rainwater company, STEPSVN, and took care of the installations.

On the Dutch side, microbiologist Johan van Groenestijn from Wageningen University & Research advised on optimising the biofilter and Casper ten Bokkel from Your Filter Factory prefabricated the treatment equipment in a sturdy steel frame, designed to fit between the water tanks. The local team only had to add the tanks and connect everything. “Together we cover all the expertise needed for water purification,” Jansen says.

An entrepreneurial response

The differences between sites were smaller than expected. Pesticide levels varied, but removal rates stayed consistent. Users have been enthusiastic across the board. “Everyone involved in the project was satisfied and wants to continue,” Jansen says. “At the university site, students even drank the water directly. The greenhouse grower was so pleased with the results that they expanded the system at their own expense after finding it collected too little water.” On top of that, a hotel manager in Can Tho has asked to host a full-scale demonstration project. “A letter of intent is currently being finalised,” according to Jansen.

Certification, then scale

The next step is certification by the Vietnamese government – a more demanding process that requires the full range of drinking water parameters to be tested, not just pesticides. Currently, the consortium is exploring various routes, including impact cluster funding and advice from the Dutch embassy, and a four-star resort in Can Tho that has offered to host a demonstration installation. Once certified, Jansen sees a role for larger technology companies to scale the system across the delta, potentially through programmes with development banks.

Looking back, Jansen is modest about the result. “I’m very glad it went so well,” he says. “After 40 years in research, I know setbacks are normal. This time, everything went remarkably smoothly. To Jansen, that shows just how much potential the innovation has in Vietnam and is reason enough to keep going: from a pilot on four rooftops to a technology that could help secure drinking water across the delta.