The Growing Carbon Footprint of Tap Water

Although recent rain and snowfall have solved some water shortages, the Metropolitan Water District of Southern California (MWD) has needed to declare several water emergencies in recent years. While much environmental attention is focused on emissions reduction, access to freshwater is also an urgent issue. Technological solutions can address many freshwater problems, but they generate significant carbon emissions.

The Problem with Freshwater

Freshwater availability in populated areas is very regional, both across the US and globally. Information from Circle of Blue and the National Environmental Education Foundation (NEEF) can be combined to provide some examples relating to water usage:

Table 1: Comparison of Freshwater Cost, Usage, Needs, and Emissions in Select US Cities

(Source: Guidehouse Insights; Circle of Blue; NEEF)

The table above highlights several important issues. First, personal water use varies by region and is unrelated to availability. Additionally, many areas that are suffering from oversubscribed water sources are expected to experience dramatic population growth. The table shows the estimated amount of extra water that will be needed daily if the new residents use the same amount as the current residents.

The Solution for Freshwater

The easiest way to collect freshwater is to take it from a nearby river or lake, when possible. Chicago, for example, has the advantage of being next to the Great Lakes, the second-largest source of freshwater in the world. Las Vegas and Phoenix, on the other hand, have minimal and overtaxed local sources. They are also forecast to experience dramatic population increases in the coming years.

This situation has not gone unnoticed, and some efforts are underway that will help, like the Drought Pipeline Project in Arizona. The go-to solution has been to restrict water use. In addition to the water emergency declared by the MWD, the Southern Nevada Water Authority has a long-term plan that primarily centers on restricting water usage. Wastewater can also be reclaimed to increase the water supply, but both Las Vegas and Phoenix already do this.

Ocean water desalination—an established technology in other regions of the world—is another option. Costs vary, but the Texas Desalination Association estimates that, in the worst case, freshwater derived from desalination costs a modest additional $0.0046 per gallon. The challenge is that Las Vegas is over 250 miles from the nearest ocean, and Phoenix is over 350 miles.

Another major challenge is the carbon emissions. The carbon footprint of desalinating seawater is up to 6.7 kilograms of CO₂ equivalent per cubic meter of water. Table 1 above shows the additional carbon emissions associated with the desalination process needed to serve the new residents forecast for Los Angeles, Las Vegas, and Phoenix. For just the two inland cities, desalination would produce more than 5,000 kilotons of additional carbon emissions annually.

This does not include the carbon generated by transportation. Pipelines offer the most economical option, but construction would emit a great deal of carbon. Using rail would double or triple the carbon emissions. And shipping water with thousands of trucks would be a carbon emissions nightmare.

Glass Half Empty or Half Full?

Building large desalination plants along with water pipelines would be costly, take many years to complete, and significantly increase carbon emissions, but it may be the only viable scenario based on the limited impact of water conservation efforts to date. There are no simple solutions to the issue of freshwater availability—only tradeoffs. Given the costs and lead times required, politicians, regulators, and the public need to start working toward a viable environmental approach to this situation, as it is too important to ignore.