As demand for water increases and water sources grow less reliable, cities are exploring new ways to protect, conserve, and reuse their existing supply. But is realistic for any city to achieve ‘net positive water’? Hanshita Rongali, a former Amane Advisors intern, recently explored the feasibility of net positive water while obtaining her master’s degree in environmental studies at the University of Pennsylvania. In this article, she shares some of her learnings and explains the challenges that prevent cities from fully embracing the concept.
When you consider the close links between water, food production, industrial activity, and economic development, it’s easy to see why no region will remain untouched by the issue of water scarcity. By 2030, the world will need 40% more water than is available – and climate change is only making it harder to predict the water cycle and mitigate against extreme events like floods, droughts, storms, and sea level rise.
Considering that more than half of the world’s population already lives in urban areas and the fact that number is likely to jump to 75% in the coming few years, cities will play an increasingly important role in managing water resources.
Leaders will be tasked with preserving freshwater sources while also meeting the needs of growing populations – and many will have to do so while relying on or replacing outdated water infrastructure.
As cities work towards improved environmental resilience, there is a need to understand how the concept of net positive water can assist leaders in building a more sustainable future. Net positive water, as defined by the EPA, refers to a system in which water consumption is limited and managed efficiently in order to return the same amount of water back to the watershed – thus, allowing for the people and ecosystem to thrive long-term.
While the push for net positive water has gained popularity within the green construction sector, and among corporates seeking to reduce their own water footprint, no cities or countries have explicitly identified a goal to achieve net zero or net positive water.
However, a guidance brief by the World Wide Fund for Nature (WWF) states the concept is rooted in the theory that if the impacts of everyone in a basin are net zero or positive, then the basin’s shared water challenges would be addressed.
While actions can be undertaken at the facility level to approach zero water impact (e.g., zero liquid discharge), achieving a ‘net positive’ facility requires additional water benefits beyond the site itself.
Building experts say there’s been a recent shift in mindset and capabilities, with larger, more complex projects – sometimes the size of small cities – offering integrated water solutions at scales not seen previously. However, there are still significant challenges in scaling from achieving net positive water at a building or site-level to true water stewardship at a city or basin-level.
During my research, it was clear that the concept of net positive water is based on the principles of aggressive water conservation, capture, reuse, and improved efficiencies. Furthermore, experts agreed that solutions need to be tailored based on the on local climate, geography, governance, and culture. The idea that ‘water is local’ was a recurring theme, with success requiring a personalized approach that is unique to each city.
The ‘local’ nature of water is where the challenge lies. The most significant hurdle to the growth of net positive water as a concept is the lack of a well-defined, agreed framework for designing, implementing, and measuring it.
Compounding the issue is the fact that water is often managed in siloes, under different categories such as stormwater, wastewater, potable water, or irrigation water and with little cross-pollination in how policies are formed, and decisions made. Another significant hurdle is that achieving net positive water at scale would likely require an overhaul of existing infrastructure.
For cities with older water infrastructure, that includes the removal, disposal, and upgrades of pre-existing systems as well as the installation of new systems. The infrastructural demands and the expense alone prompted many utility leaders to say they felt achieving net positive water was an impossible task. Additionally, federal and state guidelines limit the reuse of water in some places. Thus, if meaningful change can happen in the US, it certainly must be at the government level, driven by advocacy groups, and supported by the various city agencies and the public.
Despite there being no cities that are officially working towards net positive water, several have implemented aligned strategies, often coined as “integrated water management” or “one water” solutions.
Philadelphia’s Green City, Clean Waters program is a 25-year plan aimed at using green infrastructure to reduce the volume of stormwater entering combined sewers and expanding stormwater treatment capacity with traditional infrastructure improvements.
Since 2011, when the program first came into effect, to 2019, the green stormwater infrastructure industry grew by 13.3% and added 1,200 jobs. The program has also benefitted the local ecology, public health, and urban vitality.
San Francisco, CA
San Francisco’s Purple Pipes is another case study in effective water reuse and efficiency. The city installed pipes (which were actually painted purple) to transport water from a recycled water plant. Wastewater – known as blackwater – would be tested, treated, cleaned, vetted again, and then shipped back to the source to be reused for non-potable purposes, such as flushing toilets and irrigating landscapes.
Overall, California has seen a regional increase in recycled water production and use increasing from about 30,000 acre-feet per year in 2001 to 64,000 acre-feet per year in 2019.
Denver is currently developing strategies and policies for its One Water program. While the city already has a program which offers rebates for water-efficient toilets, irrigation controllers, sprinkler heads and other products, leaders are working on an incentive-type program that would be centered around water conservation.
While there are a few cities leading the way in building more sustainable and resilient water systems, the idea of establishing a universal definition of net positive water and a clear framework for implementation is far in the distance. I, however, choose to join the more optimistic experts that net positive water will continue to develop in its scale, scope and impact.