Desalination in the Central Coast Region

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Desalination is being considered as an alternative supply for water in Central California, where water for agricultural and residential use is in short supply.[1] In 2009, the California State Water Resources Control Board issued a Cease and Desist Order, requiring CalAm to reduce its pumping from the Carmel River by 70% by 2016 [2]. The Carmel River is the primary water source for the region, so alternative water sources are necessary. The Central Coast also relies heavily on groundwater supplies; however, problems with seawater intrusion make this an unsustainable alternative. As a result, many proposals for desalination facilities have been submitted as a possible solution to the water gap. [3] The number of operational desalination facilities in California nearly doubled in the period between 2006 and 2013. [4] A drought relief package on Governor Jerry Brown's desk proposes $6 million for desalination projects in the state. [5]

Desalination Technologies

Despite the increasing demand for potable water making desalination a more viable water supply option for many municipalities, concerns over the energy intensity of standard desalination technologies persist. A number of alternative processes and energy sources for desalination are in development.


  • Reverse Osmosis [6]
  • Forward Osmosis [7]


  • Solar Powered [8]
    • portable solar [9]
  • Reverse Osmosis - Pressure Retarded Osmosis [10]
  • Fertilizer Drawn Forward Osmosis [11]

Unit conversions

Desalination plants are generally rated in terms of Million Gallons per Day (MGD), whereas water supply planning is often accounted in Acre Feet per Year (AFY).

1 MGD = 1,120 AFY

0.5 560
1 1120
2 2240
5 5600
10 11,200

Desalination facilities in the Central Coast

Proposed and existing desalination plats in Monterey Bay. Image: MBNMS 2006




Other California Desalination Facilities

  • Carlsbad - San Diego County Water Authority and Poseidon Water, under construction, scheduled to be delivering water by late 2015, 50MGD [23] [4]
  • Huntington Beach - Poseidon Water, final permitting phase, scheduled to be operational by 2018, 50MGD [24] [4]
  • Fresno County - WaterFX (solar desal), operational, 0.014 MGD in March 2014, scheduled to produce 2MGD by 2015. [25] [26]

Main Issues

Impacts to the Marine Environment

The main potential impacts from desalination to the marine environment are impingement and entrainment of marine organisms at the water uptake as well as potential harm from the disposal of highly concentrated salt brine back into the environment [27]. Impingement occurs when fish and other organisms are trapped against inflow screens, which often results in death. Entrainment is when organisms are drawn into the facility, which are exposed to high pressures and temperatures.

Impacts to the marine environment are of particular concern in the Central Coast because the proposed facilities will operate within the Monterey Bay National Marine Sanctuary (MBNMS). The mission of the MBNMS is to protect natural resources and to implement their mission. Three of the Sanctuary's regulations are related directly to preventing impacts from desalination [28]: 1. "prohibition on discharging or depositing any material within Sanctuary boundaries", 2. "discharging materials outside of the boundaries, which subsequently enter Sanctuary waters and negatively impact MBNMS resources", and 3. "prohibition on activities that cause alteration of the seabed".

Marine impacts can be avoid or minimized with careful planning and mitigation measures. Subsurface intakes can minimize impingement and entrainment better than traditional open ocean intake methods [28]. Siting projects away from sensitive habitat or highly productive areas can also reduce the impact. To reduce impacts from brine discharge, it is recommended the brine water be diluted to a salinity of less than 5% above ambient concentration at the point of discharge [29].

Energy Consumption

Comparison of the energy intensity of California water supplies. Image: Pacific Institute [30]

The proposed desalination technologies for the Central Coast are energy intensive. Producing a million gallons of desalinated seawater uses about 15,000 kWh [30], which is equivalent to the energy use of 913 California homes per day [31]. Most of the total energy use goes towards the reverse osmosis process (70%), while pre- and post-treatment and pumping account for 13% each [30]. Pumping water from the ocean to the plant is an additional 7%.

Greenhouse Gas Emissions

The high energy consumption of desalination results in high carbon dioxide emissions. Most projects, such as the Monterey Peninsula Water Supply Project, will tap into the existing power grid. As the Central Coast transitions to renewable power sources, desalination emission estimates may decrease. Some of the theoretical emissions associated with some of the proposed desalination plants in the Central Coast are below [30]. As a reference, 1 MMT of CO2 emissions is equivilent to about one year of electricity use by 193,000 average California households [32].

Project Location Capacity (MGD) Energy Use (MWh/day) Emissions (MMT CO2e/yr)
City of Santa Cruz, Soquel Creek Water District Santa Cruz 5 75 0.007
Monterey Peninsula Water Management District Del Monte Beach, Monterey 2 30 0.0003
California American Water North Marina 10 150 0.01
Ocean View Plaza Monterey 0.25 3.8 0.003

Customer Rate Increase

The cost of desalination is falling, but remains an expensive alternative. Given the high construction and energy costs of desalination, customer water bills are expected to increase. For example, a typical customer should expect their water bills to increase by approximately 40% by 2018 if the proposed Monterey Peninsula Water Supply Project is approved[33]. Below is an estimate of what a typical customer will expect to pay with the implementation of the Monterey Peninsula Water Supply Project [34].

Monterey Water Supply Project monthly bill estimate
2013 2014 2015 2016 2017 2018
$75.74 $79.86 $88.42 $97.27 $97.38 $106.73

Regulatory Agencies



Local and Regional


  1. Monterey Peninsula Water Management District. 2011. "The Water Supply Gap."
  3. 3.0 3.1 3.2 3.3
  4. 4.0 4.1 4.2 4.3 4.4
  14. Sand City Water Supply Project
  16. City of Santa Cruz Water Department Desalination Project
  17. Ocean View Plaza Coastal Development Permit Application
  20. 20.0 20.1 20.2
  28. 28.0 28.1 Guidelines for Desalination Plants in the Monterey Bay National Marine Sanctuary 2010
  29. State Water Resources Control Board (2013) Desalination Plant Entrainment Impacts and Mitigation
  30. 30.0 30.1 30.2 30.3 Key Issues for Seawater Desalination in California
  34. Monterey Water Supply Project: California American Water updates Customer Rate Impact estimates for proposed Monterey Peninsula Water Supply Project



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