Maltese rains are often greeted with damp dismay, as rainwater runoff snakes down streets and floods low-lying areas.

But a group of local researchers believe a simple contraption allowing rainwater to seep back into Malta’s parched aquifer could ease flooding while replenishing the country’s over-extracted groundwater supply.

The concept is simple: rainwater landing on roofs drains into a medium-sized water tank and is then passed through a simple gravel filter. From there, it flows into specially-drilled recharge boreholes, or cores, which allow the water to seep back into the aquifer.

Drilled cores only reach half way to the aquifer, meaning no water can be extracted from them. The additional layers of rock also serve to further filter the seeping water from any pollutants.

The innovative project, still only half way through its two-year timeframe, was introduced to the public yesterday by project coordinator and engineer Marco Cremona.

At a lively news conference punctuated with audience questions and observations, Mr Cremona explained how the research team had spent the past year testing sample rooftops across Malta for pollutant levels.

Runoff from the first rains after summer was universally high in pollutants, with accumulated rooftop dirt the most likely culprit. But runoff water from subsequent downpours was practically pollutant-free.

“After the first rains, it would appear water is pure enough to directly recharge the aquifer,” Mr Cremona said. “And it would appear even light rainfall is enough to wash away any impurities.”

That water could then be channelled to Malta’s groundwater, which is heavily over-extracted and laden with polluting nitrates.

The research team has already drilled 15 cores at various government schools around the country. With the help of fellow engineer Adrian Mifsud, the team is currently testing them to better understand their geological composition, how well they filter out pollutants and how quickly they allow water through.

Researchers now have a year to analyse existing pollutants and come up with a cost-effective device to put on the market.

Particulate pollutants are solid and easy to filter out, while soluble ones require more elaborate filtration systems. Mr Cremona conceded that individual buildings and their owners had little to gain from installing such a device.

“The system encourages the common good. There’s no personal benefit to this, as the filtered rainwater ends up in the aquifer. But for those who have ignored planning laws and don’t have a well, or for large buildings where building a well just isn’t cost-effective, this could be ideal.”

With a target of a finished product which would be 75 per cent efficient – meaning it would filter three-quarters of the annual rainfall landing on any given roof – the research team has set itself an ambitious target.

Freak storms such as those of the past days would still result in a degree of overflow, Mr Cremona explained.

“Having a system which could handle such volumes of rainfall just wouldn’t be cost-effective, as you’d need to have significantly larger water tanks attached to it,” Mr Cremona explained.

“If all goes according to plan, in a year’s time we’ll be approaching the government with the finished product, which it could then start installing in schools and other public buildings,” Mr Cremona said.