Mini Amazons could produce London's drinking water

Stephen Cousins

Drop by Drop, a wastewater purification system, may be the answer to potable water shortages of the future

By 2025, according to the UN, London may have to recycle wastewater to provide enough drinking water for its population, so the need for more sustainable methods of water purification has never been greater.

Royal College of Art graduate Pratik Ghosh has developed a natural water filtration system, a ‘mini domestic version of the Amazon rainforest’, which he claims could be cheaply scaled up to cover residential roofs across the capital and beyond.

Drop by Drop is a vacuum pump system that transpires and evaporates water in a glass dome filled with one square foot of herbs. The proof-of-concept version is able to produce 200ml of clean water in 12 hours, but if scaled up to cover the roof of the average UK house, with a footprint of around 76m2, it could provide about 170 litres of pure distilled water in the same amount of time, Ghosh claims.

‘Rooftops are ideal because they are exposed to maximum sunlight, and they are generally underutilised,’ he says. ‘This could be done very cheaply. Rather than covering the roof with a glass dome, plants could be grown in a polytunnel.’

The prototype is based on the scientific theory of the biotic pump. This occurs in tropical areas such as the Amazon, where millions of trees and other plants drink millions of gallons of water each year, but retain only about 1% of the liquid. The rest transpires or evaporates into the atmosphere to form clouds.

‘When the water condenses it forms a partial vacuum in one layer of the atmosphere, which in turn draws more water from plants and trees and results in massive wind movements across globe,’ says Ghosh. ‘It is quite a miraculous phenomenon that expedites the process of transpiration, leading to more and more rainfall.’


The system exploits the process of phytoremediation in plants whereby contaminants such as heavy metals or nitrates are removed from soil and stored in the roots.

Ghosh passed dirty water from the Thames and the Hyde Park lake through the system, then tested it for traces of nitrates, chlorine, heavy metals and bacteria, but none were found.

‘Drop by Drop requires no maintenance at all, if you are going on vacation you just remove the pumps and plug the holes and the plants thrive without the need for watering,’ he says. But don’t expect to see a commercial version in stores any time soon – the system was developed to counter the idea of water as a commodity. ‘It’s one of the most essential requirements of being human and a basic human right,’ says Ghosh.


The B-38030 TrimLineSeries is a paper towel dispenser, automatic hand dryer and waste bin all in one

Fast worker: Bobrick's towel dispsenser, dryer and waste bin

Renowned architect of the Louvre pyramid and Museum of Islamic Art in Doha, taught by Gropius and Breuer, and whose first commission was the Mile High Center in Denver

From the Mile High Center to the Louvre pyramid and beyond