5 ways Cities can Reduce their water-related Carbon Footprint
A “carbon footprint” is a measure of the impact of an individual or community’s activities have on the amount of carbon dioxide (CO2) produced through the burning of fossil fuels and is expressed as a weight of CO2 emissions produced in tons. The burning of fossil fuels primarily comes as a result of activities related to energy use, transport, food, water use, and waste management. In 2007, it was estimated that 13% of the US’s energy consumption was from water-related energy use thus representing a significant opportunity for carbon footprint reduction. A UK study estimated the carbon footprint of water at ~0.8 g CO2 per liter of water.
The opportunities that exist to lower water-related carbon footprint are in water conservation (minimizing consumption and losses, water reuse) and environmentally-friendly water production.
Cities can focus on 5 key areas to reduce their water-related carbon footprint:
1. Low-Impact Planning & Development
While traditionally, low-impact development refers to a land planning and engineering design approach to manage stormwater runoff as part of green infrastructure, the scope can be expanded to include design measures to reduce the environmental impact of water production, distribution, consumption and treatment.
Water features such as man-made lakes, lagoons, water fountains provide substantial economic and social benefits to cities and developments, however, they should be thoroughly designed with careful consideration of source water quantity/quality and operational/maintenance requirements (e.g. energy requirements) to sustain healthy water quality. For example, to minimize water loss due to evaporation, the surface area covered by water plants on the surface of a lake or pond can be maximized.
Natural landscaping is a key element to create a functional and attractive urban center. Urban landscape designs play a vital role in improving our health/wellbeing, enhancing local biodiversity and contributing to the city’s aesthetics. A common approach to modern landscape design is xeriscaping, which is the practice of designing landscapes to reduce or eliminate the need for irrigation. Experts estimate xeriscaping can reduce irrigation water demand by up to 50%.
2. Water Production
Potable water for consumption comes from two main sources: groundwater stored in aquifers (brackish water) and surface water primarily from oceans (seawater). Brackish water has a typical salinity level of 5,000–10,000 ppm while seawater has a typical salinity level of around 40,000 ppm and the target potable water quality salinity is around 500 ppm. According to a World Bank Report, brackish water treatment requires ~1.5 kW/m3 of produced water while seawater requires ~6 kW/m3 of produced water. Where possible, cities should consider sourcing water from ground sources in order to reduce the carbon footprint associated with water treatment. However, in some cases, using groundwater faster than it is replenished (groundwater depletion) is a serious issue which contributes to carbon dioxide emissions.
If seawater is the only available source of water, cities must leverage energy-efficient processes/equipment and integrate renewable energy in the desalination process. Use of energy-recovery devices can reduce the energy requirement to produce 1 m3 of potable water from 6 kW/m3 to 4 kW/m3 or less. Additionally, if designed efficiently, solar power could be leveraged to meet a significant portion of the desalination plant’s overall energy demand. This approach is one way the Western Cape government, in partnership with France, is approaching their water crisis.
A third source of potable water is atmospheric water and a rapidly developing technology is humidity harvesting, extracting water vapour in the air through condensation. As this technology evolves, it could present an interesting opportunity for mass water production, especially if coupled with a renewable energy source. One such example is Source, which is a hydropanel that makes drinking water from sunlight and air.
3. Water Distribution
According to various experts, losses due to leakages along the water network distribution mains range from 10–40%. For a large city, this percentage could translate into a substantial volume. A common approach today is equipping the water network with smart leakage detection sensors for early and effective intervention. On a residential level, smart water meters and leakage sensors should also be installed to monitor water consumption and alert the owners or developers of possible leakages, which sometimes go unnoticed for extended periods of time.
A smart irrigation network can yield significant water savings. Typically, modern irrigation networks rely on drip irrigation which places water directly into the root zone and minimizes evaporation losses. These networks are also connected to weather stations while more advanced networks even utilize sensors that monitor soil quality and moisture levels.
4. Water Consumption
To help reduce end-user (individual) water consumption, cities should standardize low-flow fixtures in public spaces and incentivize them for private developments. Water-efficient appliances such as dishwashers and washing machines should also be encouraged as the additional initial capital investment is insignificant compared to lifecycle water savings. It is estimated that low-flow fixtures and appliances can help save up to 20–30% of water.
In the US, 56% of water-related carbon emissions are due to water heating. Thus, this represents the biggest opportunity for carbon emission reduction. Solar water heaters are the most effective way to address this, while also significantly reducing energy bills.
In order to encourage environmentally-conscious behavior related to water consumption, cities can revert to principles in behavioral economics. Cape Town has experimented with nudging to determine what type of incentives best motivate households of different income levels to reduce their consumption.
5. Water Reuse
Most cities today treat their wastewater for reuse as either potable water or irrigation water. The carbon footprint reduction opportunity that exists here is in choosing energy-efficient processes to achieve the desired water quality. In addition, for new developments that may not be connected to a centralized wastewater network, a smart approach would be to deploy temporary wastewater treatment plants onsite to avoid carbon emissions related to transporting the wastewater out of the city. New developments should also plan to ensure the treated wastewater can be used and not wasted within the development.
