Hotter, drier weather could double water bills in some cities, Stanford study finds

Hotter, drier weather threatens to double water bills by mid-century in some cities, according to a Stanford-led study. The research, published July 8 in Nature Sustainability, is the first to comprehensively model how climate change, infrastructure investment, and household water demand can combine to compound an already growing affordability crisis.

"Climate change stresses water supplies, and forces utilities to build expensive new infrastructure to maintain reliability,” said study lead author Jennifer Skerker, a PhD student in civil and environmental engineering at the Stanford Doerr School of Sustainability and the Stanford School of Engineering while working on the study. “In cities already struggling with affordability due to aging infrastructure, the additional costs passed on to ratepayers to pay for additional infrastructure and reliability measures can push a substantial share of households into crisis.”

The average cost of tap water in the United States has increased three times faster than inflation over the past two decades, driven largely by aging infrastructure and deferred maintenance. Climate change is layering a new and poorly understood pressure on top of those existing strains, according to Skerker and her study coauthors.

To understand how predicted changes in temperature and rainfall over the next two decades are likely to affect local water supplies and costs, the research team analyzed data from Santa Cruz, California. The small coastal city relies almost entirely on local surface water and a single reservoir. The local utility has implemented many lower-cost conservation options, such as water-saving appliances and reduced irrigation, necessitating infrastructure investments for climate resilience.

Using a modeling framework developed with data from Santa Cruz's water department, the researchers linked plausible future climate scenarios with utility adaptation decisions, such as building a wastewater reuse facility, methods for pricing water, and household-level water demand. Among the results: measures taken to adapt to less water availability could lead to a near doubling of median water bills in Santa Cruz by mid-century. Paying for major new infrastructure could push the share of households exceeding the EPA’s recommended affordability threshold from the 19% to 35%, according to the study’s findings.

The model showed median water bills for the poorest residents could rise from around $60 to $111 per month (in today’s dollars) under a dry climate scenario. More than 5% of households would have to devote as much as a third of their income to water, likely forcing painful trade-offs with food, healthcare, and other necessities.

Different infrastructure strategies produced starkly different outcomes. A risk-averse approach that built large desalination capacity early provided strong supply reliability, but at a steep cost to affordability. A more cautious approach that delayed investments kept bills lower but left the system dangerously exposed during droughts, providing reliable water supply in only 6 out of 10 years on average. 

The modeling framework can be adapted to assess water affordability risks in cities – such as Los Angeles, San Diego, San Francisco, Cape Town, and Melbourne, Australia – facing vulnerabilities similar to those of Santa Cruz. Even cities that seem more resilient now would do well to pay attention. They could become vulnerable over time as climate stress intensifies and utilities raise water rates, according to the researchers.

"The bottom line is that under today's financing and regulatory models, climate adaptation and water affordability are on a collision course,” said study senior author Sarah Fletcher, an assistant professor of civil and environmental engineering and a center fellow at the Stanford Woods Institute for the Environment. “Ensuring reliable water access for everyone is going to require interventions at the state and federal level that go far beyond what individual utilities can do on their own.”

Related: Achieving the human right to water in California