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Hetch Hetchy: The Engineering Marvel Behind San Francisco’s Water Security
Exec Exchange — Episode feature with Dennis Herrera, General Manager, San Francisco Public Utilities Commission (SFPUC)

In this episode of the Exec Exchange, Dr. Piers Clark speaks with Dennis Herrera, General Manager of the San Francisco Public Utilities Commission (SFPUC), about one of the most consequential and controversial water projects in the United States: Hetch Hetchy.

It’s a story that blends engineering, politics, environmentalism, climate resilience and, ultimately, leadership.

From City Attorney to Utility Leader

Dennis Herrera has been leading SFPUC for about three and a half years. Before that, he spent 20 years as the elected City Attorney for the City and County of San Francisco, effectively serving as the city’s attorney general and managing a team of 300–350 legal professionals.

That legal and policy background now underpins his leadership of one of the most complex public utilities in the U.S.:

  • US$3 billion combined operating and capital budget
  • Around 2,700 employees
  • Three enterprises:
    • Water – retail service to ~800,000 San Francisco residents and wholesale supply to a further 2.4 millionpeople in Santa Clara, Alameda, and San Mateo counties via 28 wholesale agencies
    • Wastewater
    • Power – providing electricity to ~90% of municipal load via:
      • Three hydroelectric plants in the Hetch Hetchy system
      • Additional green power from the grid through a community choice aggregation programme

Crucially, virtually all SFPUC power is non-fossil, with about a quarter of municipal needs met directly by 400 MW of hydro, and the balance procured as certified clean energy.

Climate, Fire and the New Reality for California Utilities

The conversation begins in a familiar place for California utilities: wildfire.

While this episode was recorded during major fires in Southern California, Dennis is clear that the issue is systemic, not local. The combination of:

  • Hotter, drier conditions
  • Stressed forests and landscapes
  • Strong, dry winds (Diablo/Santa Ana type)
  • Expansion of urban development into wildland areas

…creates a growing risk of “urban wildfire” that existing infrastructure was never designed to handle.

For water and power utilities, that means:

  • Higher exposure to service disruption, asset damage and public safety risks
  • Increasingly labour- and infrastructure-intensive responses
  • The need to plan not only for drought, but also for fire-driven emergencies and the knock-on effects on power, transport and water systems

It is in this climate context that the stability and resilience of the Hetch Hetchy system really stand out.

What Is Hetch Hetchy – and Why Does It Matter?

Hetch Hetchy is both a place and a system.

  • The place: a valley in Yosemite National Park, around 165 miles (265 km) from San Francisco and roughly 35–40 miles from iconic Yosemite landmarks like El Capitan.
  • The system: a 400,000 acre-foot reservoir and associated conveyance and power infrastructure that supplies around 85% of SFPUC’s regional water system needs.

It is also one of the most politically fought-over valleys in U.S. environmental history.

The Post–Gold Rush Water Problem

By the late 19th century, San Francisco’s local water sources were no longer adequate to support its growth, especially in the wake of the Gold Rush boom.

Then came the 1906 earthquake and fire, which almost destroyed the city. That disaster turned “we should find more water” into “we must secure a new, reliable source”.

Several potential sources were considered – including Lake Tahoe – but nothing stuck until Michael O’Shaughnessy, a city engineer, identified the Hetch Hetchy Valley on the Tuolumne River as a viable option.

There was one major problem: Hetch Hetchy sat inside a national park.

The Raker Act and a Political Turning Point

To develop the valley, San Francisco needed federal permission. The result was the Raker Act, a special act of Congress that:

  • Ceded rights in the Hetch Hetchy Valley to the City and County of San Francisco
  • Allowed construction of a municipal water supply and associated infrastructure within Yosemite National Park

Over roughly 20 years, San Francisco built:

  • The O’Shaughnessy Dam, creating the Hetch Hetchy reservoir
  • A 165-mile, fully gravity-fed conveyance system
  • Hydropower facilities that today form the backbone of SFPUC’s municipal green power supply

The outcome: a long-range, high-reliability water supply delivering some of the cleanest drinking water in the United States.

So clean, in fact, that SFPUC enjoys a filtration exemption from both the U.S. EPA and the California Department of Water Resources. The water is disinfected, but does not require conventional filtration before entering the distribution system.

Hetch Hetchy vs. John Muir: Where the Modern Environmental Movement Began

Hetch Hetchy is not just an engineering story; it’s a founding myth of modern environmentalism.

John Muir, the influential naturalist and founder of the Sierra Club, led a fierce national campaign to stop the dam, arguing the valley should be preserved in its natural state.

He lost the fight over the Raker Act – a defeat that deeply marked him – but the campaign itself galvanised the U.S. conservation movement. Dennis notes that many see the Hetch Hetchy fight as the birth of the modern environmental movement in the United States.

The tension is still alive today:

  • Groups like Restore Hetch Hetchy actively campaign for dam removal.
  • As San Francisco’s former City Attorney, Dennis has previously defended the city against lawsuits aimed at forcing that outcome.

For SFPUC, the challenge is one of balance:

  • On one hand, Hetch Hetchy is an irreplaceable regional water source, underpinning the Bay Area’s economic development and providing exceptionally reliable, climate-resilient supply.
  • On the other, it sits in a protected landscape with deep symbolic significance, and there is ongoing pressure to prioritise full ecosystem restoration.

SFPUC’s answer has been to partner closely with the National Park Service and the U.S. Department of the Interior, working to:

  • Maximise recreational and environmental co-benefits in and around the valley
  • While protecting the core function of the reservoir as critical drinking water and hydropower infrastructure

Eight and a Half Years of Storage: A Different Kind of Resilience

One of the most striking features of the Hetch Hetchy system is its strategic storage position.

Between Hetch Hetchy, Lake Eleanor and Cherry Lake, SFPUC can maintain around 8.5 years of water storage in the system at any given time.

That matters for several reasons:

  • The Hetch Hetchy watershed is one of the parts of California that will experience the impacts of climate change on snowpack later than others.
  • In a state where Southern California is heavily exposed to Colorado River shortages and inter-state politics, San Francisco’s supply is locally captured, locally stored and locally controlled.
  • The entire 165-mile system from the mountains to the city is gravity-fed – not a single pump along the way – which offers both energy efficiency and operational robustness in emergencies.

For water sector leaders globally, it’s an example of long-term, system-level resilience by design – built a century ago, but highly relevant to today’s climate and reliability debates.

An Engineering Marvel – and a Governance Example

Dennis calls Hetch Hetchy an “engineering marvel”, and that’s not hyperbole:

  • A high-mountain reservoir in a national park
  • A gravity-only conveyance system spanning 165 miles
  • Integrated water + power production
  • Unfiltered, high-quality drinking water at scale
  • Multi-decade storage capacity and exceptional drought resilience

For B2B audiences in the water and energy sectors, there are several strategic takeaways:

  • Integrated water–energy systems can unlock major efficiency and decarbonisation benefits, especially when hydro is part of the picture.
  • Source protection and raw water quality dramatically reduce lifecycle treatment costs and can unlock regulatory flexibilities (such as filtration exemptions).
  • Long-distance gravity conveyance remains a powerful, low-carbon design archetype where topography permits.
  • The governance story – involving Congress, national parks, environmental NGOs and municipal interests – is a reminder that large-scale water infrastructure is as much about political settlement and social licence as concrete and steel.

“Find Mentors Early”: Leadership Advice from the Top

The Exec Exchange always closes with a personal question: if you could go back 20–30 years, what advice would you give your younger self?

Dennis’s answer is simple and pointed:

“Find meaningful mentors as early in your career as possible – and soak up the knowledge and mentorship from those folks to help plot out your future career.”

He’s honest that this comes from both absence and presence:

  • Early on, he didn’t have strong mentors.
  • Later, he did – and only in hindsight did he realise how profoundly they had shaped his thinking and trajectory.

A good mentor, he says, often doesn’t announce themselves as such. You realise their impact retrospectively.

And yes – he’s very conscious that this now means paying it forward. Today, he actively mentors younger professionals – lawyers, engineers, utility staff – in the same spirit.

From contested valley to climate-resilient backbone, Hetch Hetchy is a rare combination of engineering ambition, political controversy and strategic foresight. For utilities wrestling with climate uncertainty, environmental pressure and growing urban demand, it offers both a cautionary tale and a compelling model of long-term water security.

To hear the full story in Dennis Herrera’s own words – including the politics, the litigation and the partnership with Yosemite – listen to this episode of the Exec Exchange.

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