Portfolio Solutions for Water Supply

by Jay Lund

“Water problems in the western United States, when viewed from afar, can seem tantalizingly easy to solve: all we need to do is turn off the fountains at the Bellagio, stop selling hay to China, ban golf, cut down the almond trees, and kill all the lawyers.” – David Owen (2017), Where the Water Goes: Life and Death Along the Colorado River.

Given California’s long dry seasons and tremendous variability in annual rainfall, its water supplies for cities and agriculture are surprisingly reliable and inexpensive.  This reliability has not been easy to achieve and requires constant attention (Lund et al, 2018).  In recent decades this reliability has been due to portfolio approaches employed by California’s most reliable water supply systems.

Water supply portfolios are usually considered somewhat differently than portfolios for flood management.  Water supply portfolio activities, summarized in the table below, are usually divided into water supply activities (which deliver water to users) and activities which manage or lessen demands for water use (including water conservation and water allocation actions).  However, since the time of Frontinus (97 AD), it is clear that successful water supply systems also requires cooperation from many individuals and groups who manage supplies and demands, so today’s taxonomy adds a category of incentives that encourage people involved in a water system to work well together.  (Others will propose different, perhaps better, taxonomies.)

water supply portfolio

Water supplies almost always begin with precipitation in some form.  Rarely, management actions grab additional precipitation by cloud seeding or almost never fog capture.  There is some discussion of modifying watershed to enhance runoff and make more water available to supply. These are prohibitively expensive in almost all practical applications.  Precipitation is the predominant source of water for streams and aquifers, and precipitation varies greatly seasonally and across years.  Even fossil water in aquifers originated from past precipitation.  Wastewater is increasingly thought of as an additional source of water (for reuse).

Water from these sources is rarely at the time and place when people want to use water, so it must be conveyed or stored for use, or to improve the reliability of supplies for water use.  Water is heavy and bulky, so conveyance and storage involve costs and inconvenience.  Many storage and conveyance approaches are available, and they often operate as an integrated system.

Water quality is also vitally important for many uses, so the protection of source water quality is always a concern.  Water quality is often improved with treatment, making unsuitable water suitable for additional uses.  Many forms and contexts of water treatment are available, and has become increasingly prominent.  Some American cities  now treat wastewater for potable reuse.

Water supply systems have many components which must operate well together.  Substantial improvements in costs and reliability often can be achieved by more effective operations.  In California, operation increasingly includes conjunctive use of surface and ground waters.

Water demands also can be managed.  Ideally, water use is reduced and shifted from times and places when the costs of providing additional water are not worth the value of the additional water use.  Usually we seek to reduce or shift water use from less convenient or expensive times and locations.  This is often done with water efficiency actions which modify technology (such as low-flush toilets) to provide equivalent service with less use of water.  At other times, we seek to modify behavior to change water use, such as by shortening showers or watering landscaping less.  Demand management activities can be varied for permanent, hourly, seasonal, or ad hoc reductions in water use to make water deliveries more reliable and economical.  Being able to conserve additional water during drought is a useful asset.  In principle, demand management can and should apply to all demands for water supply.

Everyone is part of and relies on a water supply system and most water systems function only if many people and interests work together.  Customers must pay water bills, maintain their plumbing, not steal or over-use water, maintain water quality, and reduce use more during droughts or other shortages.  Local water utilities and their contractors must safely, effectively and efficiently operate distribution infrastructure.  A host of regional water wholesalers (e.g., MWDSC, SWP, and CVP in California), water sellers, and a variety of service, material, equipment, and operating contractors are essential to most water systems in California.  This need for many people and organizations to work well together requires suitable mutual expectations, inspections, standards, and enforcement of approximate compliance with mutual expectations.  Any water system will collapse without effective incentives to work well together, enforced mutually and by governmental powers.

Portfolio approaches that artfully combine these many elements cannot eliminate conflicts among water users and conflicts across water management purposes (such as among water supply, flood, and ecosystem purposes).  Indeed, portfolio solutions will sometimes cause some new conflicts and trade-offs.  However, water supply portfolio solutions should reduce overall water supply problems and provide greater reliability at less cost and conflict than would likely occur otherwise.  Indeed, adopting portfolio solutions for all major water management purposes would likely reduce conflicts across purposes, as portfolio solutions usually are far more flexible and adaptable.

Portfolio solutions are more complex than simple and less adaptable water supply solutions in the past.  These more complex solutions require more complex institutional arrangements and analysis, using computer modeling, to provide assurances that components will work well together over a range of conditions.  The additional noisiness and controversy from these analysis and negotiations belies the typically greater reliability of portfolio management – it is often the sound of relative transparency and people paying attention.

Effective water supply portfolios also vary with time and conditions.  California’s San Joaquin Valley is going through painful portfolio changes arising from the state-mandated end of groundwater overdraft, increases in environmental flows, and the expansion of profitable tree crops (Hanak et al. 2019).

One last point is the role of portfolios within each sector for making agreements to improve performance across water management purposes.  An example is the agreement for operating Folsom Reservoir outside Sacramento, California for both water supply and flood control.  The dam operator, the US Bureau of Reclamation – mostly concerned with water supply, contracts with a local flood control authority (the Sacramento Area Flood Control Agency) to lower the reservoir more in winter to reduce flood risk, and is compensated for water deliveries lost in years when the lower winter storage results in less water supply being available.

There is a common saying in California water these days that, “There is no silver bullet, only silver buckshot.”  But effective water management is unlikely to result from a shotgun blast of disintegrated actions.

Further Reading

Frontinus, Sextus Julius (97 AD), The Water Supply of the City of Rome.  An 1899 translation by Clemens Herschel was published by the New England Water Works Association (1973)

Ellen Hanak, Alvar Escriva-Bou, Brian Gray, Sarge Green, Thomas Harter, Jelena Jezdimirovic, Jay Lund, Josué Medellín-Azuara, Peter Moyle, and Nathaniel Seavy (2019,” Water and the Future of the San Joaquin Valley, PPIC, San Francisco, CA, February.

Lund, J. (2019), “Portfolio Solutions for Water – Flood Management,” 3 March, CaliforniaWaterBlog.com

Lund, J.R., J. Medellin-Azuara, J. Durand, and K. Stone, “Lessons from California’s 2012-2016 Drought,” J. of Water Resources Planning and Management, Vol 144, No. 10, October 2018.

Maven’s Notebook, More reliable water supplies for California: Building a diverse regional water supply portfolio.

White, Gilbert (1966), Alternatives in Water Management, Publication 1408, National Academy of Sciences – National Research Council, Washington, DC, 52pp.

Jay Lund is a Professor of Civil and Environmental Engineering at the University of California, Davis.


About jaylund

Professor of Civil and Environmental Engineering Director, Center for Watershed Sciences University of California - Davis
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5 Responses to Portfolio Solutions for Water Supply

  1. Frances Griffin says:

    Successful? The salmon runs are pathetic and some may disappear. “They are poisoning the land in the Central Valley and subsidence is more and more common. I do not call that successful.

  2. Jai Rho says:

    “. . . kill all the lawyers.” Sounds funny, but the joke is actually on those who misinterpret the line. When Dick the Butcher made that suggestion in Shakespeare’s Henry IV, he was proposing a way to disrupt law and order — not end corruption as many people mistakenly believe.

    Analogously, it would be a mistake to exclude new sources of freshwater, such as desalination and fog harvesting, from California’s water supply. Less than 1% of the Earth’s water is freshwater in the form of rivers, lakes, streams, groundwater, snowpack, etc. and about 2% is frozen in glaciers and the polar ice caps. 97% of the planet’s water is in the ocean, and California has 840 miles of coastline.

    The Carlsbad desalination plant can produce 50 million gallons of freshwater per day, and larger plants such as the Ras Al Khair Desalination Plant in Saudi Arabia can produce more than 200 million gallons of freshwater per day. Many people protest that desalination is too expensive — the cost of freshwater at the Carlsbad plant is about $2,000 per acre foot — but the cost per gallon is substantially less than 1 cent (Carlsbad water is 0.6 cent/gallon) and should decrease as technology and infrastructure advances. By contrast, many people pay $1.00 or more for 12 oz of bottled water, which is equivalent to $10.00 per gallon or more.

    Fog harvesting is also a promising source of freshwater. Scientists at MIT and UC Berkeley are currently developing potentially high-yield systems that absorb humidity with porous materials known as metal-organic frameworks (MOFs) and release water vapor with solar power, which then condenses into liquid freshwater.

    Let’s be smart, develop new sources of freshwater and save the lawyers.

  3. J Rizzi says:

    Toilet to FARM — connecting largest users with large source of water for reuse. Toilet to tap is just gross & many have trust issues with water industry to get it right 100% of time.
    Delta SALT DIET — Density Driven Salty Sea Water drives Salt into Delta, but shipping channel salt locks will increase our fresh water and improve our Delta environment.

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