Our planet’s most distinctive feature is the blue that surrounds our land. This is what earned it its name “Pale Blue Dot” among planets of our solar system in a photograph taken in 1990 by the Voyager 1 space probe[sc:1]. But even though around 71% of Earth is covered in water, 96.5% of that is salty ocean water which is not suitable for drinking[sc:2].
Given the importance of drinking water for sustaining life on Earth and the increasing occurrences of drought due to climate change, technologies for cleaning water so that it can be consumed safely have never been more important. Unsurprisingly – though very much regrettably – today’s water crisis disproportionately affects the world’s poorest with water-related diseases impacting more than 1.5 billion people every year particularly in developing countries.
But the impacts of water shortages are also being felt across the Western world; for example, the most recent drought in Cyprus lasted four years (2004 – 2008) causing reservoir levels on the island to plummet. The government had to cut the supply of water giving households only just enough water to live on; fines were introduced for those using more than their share. At the height of the crisis, the Cypriot government imported 8 million cubic meters of water from Greece at a cost of over €40 million (US$43.4 million) [sc:4].
Beyond ensuring we use water as efficiently as possible, technologies that can help clean water so that it can be consumed safely will become increasingly relevant not only for overcoming water scarcity but also for addressing global challenges such as eradicating poverty and malnutrition. While some of these technologies are costly and can create other environmental damage, there are a number of green ways to clean water for drinking that should be explored.
The miracle tree
Many solutions are based on the natural properties of different elements and materials to clean water. One such technology involves using the tree Moringa oleifera, coined the miracle tree. While initial studies indicated that the process would be too expensive or not feasible for producing water which could be stored, researchers from Pennsylvania State University were able to use the seeds of the miracle tree for achieving the same result. Their study found that a substance in the miracle tree’s seeds can bind to sediment and kill microbes when used in conjunction with negatively charged sand[sc:5].
Another widely used method that has several applications is using the sun to help purify water. The sun plays an important role in the water cycle so naturally scientists have discovered several ways to use the sun’s energy and the processes of evaporation and condensation to help sanitize water and make it safe to drink. A relatively simple and inexpensive method is using solar stills. The technology is fairly rudimentary as one of the first solar stills was used as early as the 19th century in Chile to provide drinking water to mine workers.
Today, the Suns River Sill (SRS) which runs on renewable energy providing water can be used for both drinking and agriculture. The SRS can produce around 20 litres of water per square meter of floor surface compared to just 4 litres per square meter for standard solar stills[sc:6]. There are also more personalised solutions, for example the Watercone can provide up to 1.5 litres of clean water per day by absorbing sunlight and heating up the water[sc:7].
A third exciting technology involves the use of salt. Using the sun to disinfect water works primarily on water that is clear – or relatively clear. However, in most regions where water scarcity is high, the available water tends to be murky. So the first step should be to remove the clay particles through a process called flocculation.
Joshua Pearce, associate professor of materials science and engineering at Michigan Technological University worked with student Brittney Dawney of Queen’s University in Ontario to discover that sodium chloride, in other words simple table salt, can do this job very well. When added to muddy water, salt binds with clay particles and settles to the bottom of the water container.
It’s then easy to strain the water and remove the mud so that the water can be further purified using sun-based technologies. What is more the water does not become overly salty, it has a lower sodium concentration than Gatorade, so it can still be used for drinking when other water sources are not available.