November 2022 -- What does carbon-friendly SDG6 look like? 

Sustainable Development Goal 6 is "Ensure availability and sustainable management of water and sanitation for all." This follows on the heels of Millenium Development Goal 7.C, which aimed to cut in half the number of folks without access to safe drinking water and sanitation. Remarkably, the UN reports that that goal was met five years ahead of schedule, and that 2.6 billion people gained access to improved drinking water sources between 1990 and 2015. 

So if MDG 7.C was so successful, what drives SDG6? Well, two things. First, OurWorldInData reports that nearly 6% of the planet still lacks access to an improved water source. Second, access to improved water sources is proving to be an imperfect measure of access to safe water (UNICEF and WHO, 2011). The UN reports that nearly 2 billion people still don't have access to a safely managed water source, which means that water treatment is likely to grow substantially in the coming decades. As someone deeply interested in the global transition from improved water sources to safe water available for everyone, I have spent a number of years thinking about what kinds of water treatment are most suitable and useful in different industrialized and industrializing contexts. 

Some years ago, I had the opportunity to work with Drs. Maggie Busse and Chip Blatchley at Purdue on a project trying to understand this question from one particular perspective - comparing the environmental impact of different treatment technologies. To do this, we used life cycle assessment and examined the cradle-to-grave (resource extraction to product disposal) impacts of several technologies which utilized the power of the sun to produce safe water. The results of that analysis were published this month in Environmental Science& Technology. 

So what did we find? Well, we found that it's hard to beat the environmental impact of just chlorine per cubic meter of water. Two different types of UV treatment and several kinds of SODIS bag all remained far more competitive with chlorine than a parabolic collector (direct disinfection with sunlight), and delivery of water with a lorry, which is popular in many locations today, proved a bad match for environmental sustainability. 

Beyond "chlorine wins", what should we remember? Well, interestingly, low-pressure mercury UV lamps outperform LED lamps for now, largely because of the material-intensive nature of early-stage LED lamps. Furthermore, the material used for SODIS bags (and their corresponding longevity) plays a huge role in determining the environmental impact of the bags, and it might be worth considering large-scale manufacturing of PMMA bags if we want to reduce the environmental impact of SODIS. Finally, it's worth remembering that chlorine has proven a troublesome treatment technology in many parts of the global south, where the taste of chlorine is enough to drive folks away from newly built safe water systems. So while the environmental impact of treatment technologies is an interesting and useful consideration, there are many other variables which will go into choosing the best path to SDG6. 

Check out the full article at ES&T: 

Busse, Margaret M., Jason K. Hawes, and Ernest R. III Blatchley. “Comparative Life Cycle Assessment of Water Disinfection Processes Applicable in Low-Income Settings.” Environmental Science & Technology 56, no. 22 (November 15, 2022): 16336–46.


UNICEF and WHO. “Drinking Water Equity, Safety and Sustainability.” New York, NY: UNICEF andWorld Health Organization, 2011.