Throughout my childhood, I was lucky enough to spend most of my summers on the Costa Del Sol. Coming to the end of the school term and knowing that a month of swimming, sunbathing, and eating Spanish food with my family was an unrivalled holiday experience. As kids, we were always warned off drinking the tap water, instead buying, and drinking bottled water. We also told each other stories that if you so much as let a drop of water from the shower into your mouth you would also get very sick. At the other end of the scale, we learnt very young that the water in the swimming pool was so heavily chlorinated that opening your eyes under water would result in redness for the rest of the day. All of this was far removed from our experiences back home in Ireland, but we didn’t pay it much attention, its just how it was.
On one day of my holidays in a café in Fuengirola, I found myself next to a table of two men. One man, I think a local, spoke in perfect English to a man who I later learnt had just moved to the Costa Del Sol from England to join the nomadic community here on the Costa. Between them on the table were two coffees and a sheet of paper. The sheet consisted of a hand drawing of a sort of travelling home. The drawing showed an all in one bed, chair, dining table, with solar powered chargers and storage space positioned across the home for all their travelling needs. As these men chatted about the nomadic home, it became apparent that the most important and interesting aspect of the design revolved around how they used their water to maximize efficiency. The water they stored to drink was different to the water they used to shower, the shower water itself mounted on the roof of the nomadic home to stay warm. The runoff water from the shower was collected to use for washing the home or else to dispose of at the next drain. As I sat eavesdropping on their plans, I realized it sat in complete contrast to my own experiences on the Costa Del Sol, drinking only bottled water, showering morning and night and by the pool side – the pool itself a reservoir of water with only one purpose and certainly not a use these nomadic travelers would feel at all necessary or efficient. Coming from Ireland, and perhaps readers from Northern Europe or countries with a similar climate will empathize, I had never really considered the need to make use of water in this cascading fashion. I wash, drink, flush and swim in water from essentially the same source, all initially of drinkable quality. Now, I am not advocating the need for water reuse at the scale these men were doing, but it was certainly an eye opener for me and introduced me at an embarrassingly old age to the concept of water reuse and water quality for different applications.
Fresh water is also not our only option of accessing more water for use across the globe. Salt water can be purified through desalination to achieve potable water. There is a passage from the book, Life of Pi where Pi discovers twelve solar stills in a survival locker. He takes the solar stills, fills them with salt water and leaves them to evaporate and simultaneously collect condensate in a separate vessel, helping Pi to survive in this section of his adventure. This is one of the few instances in the book where Pi successfully makes use of a man-made survival tool. Although a solar still is shown in the film, I do not believe much attention is drawn to its operation, however the book has at least demonstrated this technology to a wide audience of readers. Our nomadic travelers may not have considered this yet, or at least did not discuss it during the brief excerpt of their conversation I overheard, but it would complete the water cycle for them and in turn make them entirely self-sufficient for their water needs. So, what can we learn about water reuse across the globe from Pi and our survival experts? Although these examples are small scale, they do cover many of the segments of technology available and in use today for water reuse.
When reusing water, some treatment may be required before the water is of a suitable standard depending on the next application. For example, there may be instances where water used to clean agricultural equipment could immediately be used in irrigation, but there wouldn’t be many instances where reused water could be provided without treatment as drinking water. The degree of treatment required between one application and another will dictate the equipment required. In wastewater treatment plants, there are three levels of treatment: Primary, which will remove large, insoluble contaminants through techniques such as screening, secondary which combines physical and biological techniques such as sedimentation and activated sludge treatment, and finally tertiary treatment which will typically consist of chemical and biological treatment techniques to disinfect the water stream, using techniques such as UV irradiation to damage organisms and the addition of free radicals such as chlorine to oxidize organic material. For water being returned to waterways or used in some water reuse applications, secondary treatment will be sufficient to ensure, once diluted, the effluent is safe for the environment. For instances where water will be used for sanitation or consumption (often referred to as potable water) tertiary treatment will be required.
The agricultural sector is one of the hardest hit sectors by water scarcity, as it withdraws 70% of freshwater reserves globally and consumes 90% of all available water supplies globally . So, there is an obvious need to increase the efficiency of water used in agriculture by improving the reuse of water. At the same time, climate change and increasing global populations are putting more strain on water resources as the demand for food and water increase. There are thankfully many opportunities for water reuse across industries, but particularly in the agricultural sector. Effluent from primary treatment is suitable for irrigation on parklands and forests, whilst water that has undergone secondary water treatment can be used to irrigate crops indirectly, for example in the irrigation of olive trees- the rule here being that water should not come into direct contact with foodstuffs. In both cases, the environment the water is introduced to acts as an environmental buffer before flowing to waterways that are used as sources for drinking water supply. Tertiary treated water can be safely discharged from site or potted for a range of sanitary uses. On a farm, tertiary water can be used to directly irrigate crops or for consumption by livestock.
Water reuse for agricultural purposes is particularly popular in regions suitable for crop growth but equally prone to drought. As climate change progresses, instances of drought become more common and more widespread. Thus, water reuse will need to be used in more regions. Parts of California, USA adopted indirect water reuse in the 1950’ and 60’s as a means of improving the efficiency of water use and securing their limited water supply. Orange County, California has a flagship water reuse facility which recently broke a world record for the amount of water cleaned and stored for potable water use, recycling more than 100 million gallons of water in a 24-hour period . The water is of ‘near-distilled’ quality, with minerals added to improve taste. Even with such high-quality water supply, Orange County has faced issues with perception of water cleanliness given it has been cleaned from previous uses, rather than being withdrawn from a reservoir. This perception issue is often termed ‘the yuck factor’ and is a problem faced globally.
The most famous example of a water reuse project facing resistance due to the yuck factor occurred in Toowoomba, Australia. In 2006, during the Millennium Drought, Toowoomba was forced to consider treating sewage and sending it to a dam for reuse as potable water. Resistance to the idea quickly gained momentum, with an opposition group forming and forcing the local council to send the decision to a referendum. The group opposed to the water reuse appealed strongly to the yuck factor concept, naming their group ‘Citizens against Drinking Sewage’ and labelling the region ‘Poowoomba’ . The example of Toowoomba demonstrates that even though the technical capability exists to reuse water, even to the point that it is now cheaper to reuse water than to withdraw water in Orange County, perhaps the more challenging aspect of water reuse is overcoming the misconception that reusing water is somehow unsafe or unhygienic in countries used to high levels of sanitation.
The REWATERGY project’s core objectives are to (1) enhance the energy recovery from wastewater, (2) improve the energy efficiency of water disinfection, and (3) increase the resilience of distributed household safe drinking water systems. Objectives two and three are concerned with water reuse, with the project aiming to develop prototypes for each of these objectives. The prototypes for objective two use technology that has shown promise as chemical free, highly efficient alternative to conventional tertiary treatment techniques, namely UVA LED photoelectrocatalysis. A prototype for objective three will incorporate a membrane sufficiently sized to remove microplastics from water streams with UVC LED technology to disinfect pathogens present in the water. Although the intended market of each of these prototypes potentially straddle the spectrum of water treatment applications (objective two prototypes are likely suitable for industrial, agricultural, or pharmacological waste streams, whilst the objective three prototype will be suitable for point of use), they could both have a role to play in improving water reuse. The objective two prototype’s main strengths in the industries named above would be the minimal operator input in an organization not otherwise trained in wastewater treatment processes, the long lifetime of a UV LED based system and the potentially broad range of treatable contaminants make it a sound solution for water treatment and reuse. The objective three prototype is an ideal solution for countries with mains water supply that is not suitable for consumption. By using membrane technology to filter out microscopic contaminants first, then treating pathogens in suspension, water can be upgraded for drinking and other potable water applications.
Going forward, water use practices will need to become more focused on reuse and efficiency as prevalence of drought and demand for food and water increase. All industries, in particular the agricultural sector, must leverage water reuse. Technology that makes this simple and financially viable to the sector is of particular importance to drive water reuse as a practice. The first time Pi turned on a tap, he observed, “its noisy, wasteful, superabundant gush was such a shock that my legs collapsed beneath me and I fainted in the arms of a nurse”. To protect our water resources, we must not be wasteful.
 D. Norton-Brandao, S.M. Scherrenberg, J.B. van Lier, Reclamation of used urban waters for irrigation purposes – a review of treatment technologies, J. Environ. Manage., 122 (2013), pp. 85-98, 10.1016/j.jenvman.2013.03.012
 From waste to taste: Orange County sets Guinness record for recycled water, Orange County Register, https://www.ocregister.com/2018/02/18/from-waste-to-taste-orange-county-sets-guinness-record-for-recycled-water/ Accessed: 2020-10-07
 Toowoomba says no to recycled water, https://www.smh.com.au/national/toowoomba-says-no-to-recycled-water-20060731-gdo2hm.html Accessed: 2020-10-07