in 2017, the theme was "why waste water?" which was about reducing and reusing wastewater. the theme was a play on words as it related to both the aspect of wasting water and issues around wastewater, namely treatment and reuse. wastewater is a valuable resource to help achieve the sustainable development goal number 6. one aspect of target 6.3 is to halve the proportion of untreated wastewater and also to increase the recycling and safe reuse of water across the globe. after appropriate treatment, wastewater can be used for a variety of purposes. industry, for example, can reuse water in cooling towers and agriculture can reuse water for irrigation.