Why wastewater holds the key to building climate-resilient cities

At the annual United Nations climate change conference in Glasgow, the first-ever" Water for Climate pavilion highlighted how closely aligned climate and water policies are. The goal was to push world leaders to prioritise building climate-resilient water infrastructure and services. This is particularly salient in countries like India, where green-field urban growth is just beginning.

Urban development is contingent on the availability of water. Historically, the approach has been to go farther in search of new water sources or pump deep groundwater. But these sources are energy-intensive - the water must be pumped over long distances or from great depths. Moreover, this also exacerbates water insecurity in the rural watersheds from which they are sourced.

We are running out of sources to tap, and groundwater is getting depleted. We have to look elsewhere for solutions. Part of the answer lies in integrated urban water management, which prioritises wastewater treatment and effective reuse.

Water management and climate change

Water management in cities will be even harder under climate change, with the increasing frequency of extreme events. At the same time, the demand for water is likely to increase; the likelihood of more intense heat waves makes the need for green spaces more urgent.

Indeed, many cities are attempting to build resilience by increasing green cover, with the latest example being the Delhi Masterplan. The Bangalore Development Authority is working on a draft city masterplan that prioritises greening. The main objective of these initiatives is carbon sequestration. The problem is that green spaces need to be irrigated and, frequently, the water source is deep borewells. This is not sustainable and puts pressure on scarce freshwater sources that might instead be used for drinking.

These trends raise important questions. How are we going to source water to meet the needs of a rapidly growing urban population? How do we restore and expand vanishing green spaces critical for recharging groundwater, reducing flood peaks, and adapting to rising temperatures?

Wasted potential

Our studies have explored the potential of reusing treated wastewater from apartment sewage treatment plants as an alternative source of freshwater for various non-potable uses. Since 80 per cent of water supplied to cities returns as wastewater, treating and reusing a portion of this holds tremendous potential. The state of Bengaluru's water and sanitation system is already precarious - 40 per cent of residents lack access to piped water, 50 per cent of households lack access to sewer lines, and 40 per cent of the city's sewage is untreated. Even the little treated does not make its way back to the cities as it is released into drains and water bodies.

We need to push for more circularity so that this common-pool resource that is being wasted and privately controlled can be used for the public good. This is particularly relevant at a time of such acute water scarcity, worsening pollution of public lakes and wetlands and uncontrolled urbanisation that's encroaching on what's left of our urban green spaces.

Currently, the centralised sewage treatment plants (STP) in Bengaluru can treat 721 MLD (million litres per day) of sewage, while decentralised plants treat 110 MLD. But 288 MLD, or 40 per cent of this 721 MLD capacity, is underutilised due to the lack of sewerage infrastructure connecting the sewage to STPs. The total untreated sewage in Bengaluru city amounts to 660 MLD.

State agencies have made concerted efforts to push for decentralised sewage management to plug this large gap. For example, the Bangalore Water Supply and Sewerage Board (BWSSB), through a notification issued in 2016, mandated that all residential projects with 50 units and more, commercial projects (with a built-up area of 2,000 sq. mts. and more) and educational institutions must install and ensure reuse of treated water.

But despite these strict measures, wastewater continues to find its way into our lakes, and we continue to dig deeper borewells to source depleting freshwater. We wanted to understand why even the 50 per cent of wastewater that is getting treated in apartments was also going unused, despite there being zero discharge laws in place. So we spoke to apartment residents, builders, STP operators across 15 different wards in Bengaluru to understand why this was happening.

The 'yuck' factor, poor monitoring

One of the big reasons for this is a negative perception and lack of trust in treated wastewater among residents. Insufficient checks and balances to ensure the quality of wastewater further eroded confidence in this resource. Only three out of the 20 RWAs we interviewed were monitoring their STPs on a monthly basis.

However, most people were currently willing to reuse treated wastewater for landscaping. This presents as an ideal solution also because the current level of treatment and the quality of treated wastewater makes it suitable for greening as it is low in chemical contaminants and high in organic content.

The 'grey to green' solution

Using treated wastewater for greening public spaces circumvents that big hurdle associated with its use - the yuck factor. Aside from this, using treated wastewater for greening can also yield multiple benefits in terms of climate mitigation and adaptation. Green spaces are, in fact, critical for low carbon development. Trees and plants sequester carbon, but they also improve walkability and quality of life. Along roadsides and highways, avenue trees reduce the impact of extreme heat events, which benefit the poor who walk the most. 

The amount of water required to irrigate urban green spaces in Bengaluru is around 35 million litres of water every day, and currently, it is freshwater that is being used. Our analysis found that 20.1 billion litres of treated wastewater is available in Bengaluru every year. If we effectively utilise this to green public spaces, we can potentially consume 63 per cent of this wasted resource.

Redirecting wastewater for this purpose, especially in the dry months, also means that this water no longer flows into our lakes - the city's vital 'blue infrastructure' - where it hinders the water bodies' ability to act as a flood buffer as they are perennially full. This contributes to urban flooding.

Therefore, reimagining how we use treated wastewater is essential as it can restore urban green spaces and manage floods. This isn't a distant pipe dream. The BWSSB has installed STPs in two of the city's most famous parks — Cubbon Park and Lalbagh. The capacity of the STP is 4 million MLD and 1.5 MLD in Lalbagh and Cubbon Park, respectively. The wastewater output generated is sufficient to water each of these parks and green spaces in the neighbourhood.

The challenges to be overcome

Several challenges need to be overcome before a 'grey to green' solution can become a reality. Wastewater may not always be generated at the time and place where it can be used. So issues of transportation (getting the wastewater from the generation to the point of use), storage (safely storing it for a short period before it can be used), safety (ensuring that the greywater is free of pathogens and suitable for the end-use intended), and seasonality (finding uses for wastewater in the rainy season when demand for irrigation is minimal) need to be solved.

One option is partnering with start-ups like Tankerwala, an e-commerce platform, to implement a pilot programme whereby treated wastewater from apartments can be used in green public spaces and medians in the area.  But it will also require the cooperation of many stakeholders, including start-ups like the Foundation for Environmental Monitoring (FFEM), who can establish water quality cheaply, and BBMP and BWSSB to establish the acceptability of wastewater markets.

When this is scaled across a city like Bengaluru, it will save 35 MLD of water and provide freshwater access to 500,000 people. Across five Indian cities, this could be 205 MLD of freshwater saved, benefitting 2.25 million people.

Solutions to our seemingly intractable urban challenges exist, but they require diverse players to collaborate to effect innovations in socio-technical systems. This will be critical if Indian cities are to become less vulnerable to the devastating impacts of climate change.

(The writer is a researcher under the Green Cities Initiative at the Centre for Social and Environmental Innovation at ATREE, Bengaluru)

Disclaimer: The views expressed above are the author's own. They do not necessarily reflect the views of DH.