Most human activities that use water produce wastewater. As the overall demand for water grows, the quantity of wastewater produced and its overall pollution load are continuously increasing worldwide.
In all but the most highly developed countries, the vast majority of wastewater is released directly to the environment without adequate treatment, with detrimental impacts on human health, economic productivity, the quality of ambient freshwater resources, and ecosystems.
Although wastewater is a critical component of the water management cycle, water after it has been used is all too often seen as a burden to be disposed of or a nuisance to be ignored.
The results of this neglect are now obvious. The immediate impacts, including the degradation of aquatic ecosystems and waterborne illness from contaminated freshwater supplies, have far-reaching implications on the well-being of communities and peoples’ livelihoods.
Continued failure to address wastewater as a major social and environmental problem would compromise other efforts towards achieving the 2030 Agenda for Sustainable Development.
In the face of ever-growing demand, wastewater is gaining momentum as a reliable alternative source of water, shifting the paradigm of wastewater management from ‘treatment and disposal’ to ‘reuse, recycle and resource recovery’. In this sense, wastewater is no longer seen as a problem in need of a solution, rather it is part of the solution to challenges that societies are facing today.
Wastewater can also be a cost-efficient and sustainable source of energy, nutrients, organic matter and other useful by-products. The potential benefits of extracting such resources from wastewater go well beyond human and environmental health, with implications on food and energy security as well as climate change mitigation. In the context of a circular economy, whereby economic development is balanced with the protection of natural resources and environmental sustainability, wastewater represents a widely available and valuable resource.
The outlook is undeniably optimistic, provided action is taken now.
The world’s water: Availability and quality
Globally, water demand is predicted to increase significantly over the coming decades. In addition to the agricultural sector, which is responsible for 70% of water abstractions worldwide, large increases in water demand are predicted for industry and energy production.
Accelerated urbanization and the expansion of municipal water supply and sanitation systems also contribute to the rising demand.
Climate change scenarios project an exacerbation of the spatial and temporal variations of water cycle dynamics, such that discrepancies between water supply and demand are becoming increasingly aggravated. The frequency and severity of floods and droughts will likely change in many river basins worldwide. Droughts can have very significant socio-economic and environmental consequences. The crisis in Syria was, among other factors, triggered by a historic drought (2007–2010).
Two thirds of the world’s population currently live in areas that experience water scarcity for at least one month a year. About 500 million people live in areas where water consumption exceeds the locally renewable water resources by a factor of two. Highly vulnerable areas, where non-renewable resources (i.e. fossil groundwater) continue to decrease, have become highly dependent on transfers from areas with abundant water and are actively seeking affordable alternative sources.
The availability of water resources is also intrinsically linked to water quality, as the pollution of water sources may prohibit different type of uses. Increased discharges of untreated sewage, combined with agricultural runoff and inadequately treated wastewater from industry, have resulted in the degradation of water quality around the world. If current trends persist, water quality will continue to degrade over the coming decades, particularly in resource-poor countries in dry areas, further endangering human health and ecosystems, contributing to water scarcity and constraining sustainable economic development.
Wastewater: Global trends
On average, high-income countries treat about 70% of the municipal and industrial wastewater they generate. That ratio drops to 38% in upper middle-income countries and to 28% in lower middle-income countries. In low-income countries, only 8% undergoes treatment of any kind. These estimates support the often-cited approximation that, globally, over 80% of all wastewater is discharged without treatment.
In high-income countries, the motivation for advanced wastewater treatment is either to maintain environmental quality, or to provide an alternative water source when coping with water scarcity. However, the release of untreated wastewater remains common practice, especially in developing countries, due to lacking infrastructure, technical and institutional capacity, and financing.
Wastewater, sanitation and the sustainable development agenda
Access to improved sanitation services can contribute significantly to the reduction of health risks. Further health gains may be realized through improved wastewater treatment. While 2.1 billion people gained access to improved sanitation facilities since 1990, 2.4 billion still do not have access to improved sanitation and nearly 1 billion people worldwide still practice open defecation.
However, improved sanitation coverage does not necessarily equate with improved wastewater management or public safety. Only 26% of urban and 34% of rural sanitation and wastewater services effectively prevent human contact with excreta along the entire sanitation chain and can therefore be considered safely managed.
Building on the experience of the MDGs, the 2030 Agenda for Sustainable Development has a more comprehensive goal for water, going beyond the issues of water supply and sanitation.
SDG Target 6.3 states: By 2030, improve water quality by reducing pollution, eliminating dumping and minimizing release of hazardous chemicals and materials, halving the proportion of untreated wastewater and substantially increasing recycling and safe reuse globally. The extremely low level of wastewater treatment reveals an urgent need for technological upgrades and safe water reuse options to support the achievement of Target 6.3, which is critical for achieving the entire Agenda. The efforts required to achieve this Target will place a higher financial burden on low-income and lower middle-income countries, putting them at an economic disadvantage compared to high-income and upper middle-income countries.