California Water Reservoirs Part 4: Water Reclamation and Conservation

Precipitation into California watersheds and groundwater from aquifers are the main water resources for California. Water is the most important resource for any society. With droughts passing us by in recent memory (i.e. 2020-22 and 2011-2017 [1]) and the heavy rains in 2023 in California, folks had asked, "how can we capture all this rain?" [2]. Precipitation that falls into a reservoir's watershed is a fairly solved problem - we're going to utilize that water! The precipitation that is considered stormwater, water that often needs to be managed to prevent flooding [3] damaging urban and agricultural areas. Cities often have stormwater infrastructure (e.g. retention ponds, detention areas, etc.) that helps prevent flooding; and sometimes the infrastructure can be used for capture to recycle it for use in our water supply. Stormwater often needs to be processed as the water has pollution and urban runoff - this can make stormwater expensive to recycle; and yet, we see urban areas are willing to pay top dollar for water.

The name of the game is to catch as much water as possible but also how to use it effectively. That leads us to two flavors of questions:

  1. How can we capture and recycle stormwater, greywater, and wastewater?
  2. How can we conserve and manage our water usage in agriculture?

I'll focus on the first question only. The second question - as mentioned in the previous blog post - is beyond the scope of this set of blog posts.

Capturing and Recycling Stormwater and Wastewater

Early in his time in office, Governor Gavin Newsom issued an executive order to create the Water Resilience Portfolio [4]. The policy initiatives outlined in it and the 2022 Water Supply Strategy [5] detail some ideas to the extent of what California plans for stormwater capture and wastewater. This table below shows the additional acrefeet projected for stormwater capture and wastewater recycling by 2030 and 2040 in acrefeet:

Stormwater*250,000 Acrefeet500,000 Acrefeet
Wastewater Recycled800,000 Acrefeet1,800,000 Acrefeet

Note that stormwater agencies are likely not able to recycle all of this captured water but instead recharge groundwater basins.

By 2030 California aims to capture and recycle up to a little over 1 million acrefeet combined of stormwater, greywater, and wastewater and 2.3 million by 2040.


The 2022 Water Supply Strategy [5] document focuses primarily collecting, retaining, and detaining stormwater in urban areas. The aim is to have an additional supply capacity of 250,000 acrefeet by 2030 and 500,000 acrefeet by 2040. That might not seem like a lot but 500,000 acrefeet is about the amount of water used by Los Angeles per year [6]. It would behoove the large metros in California to go beyond the State goals for 2030 and 2040. Imagine if the metro areas (and the local municipalities working together) capture and recycle up to a very large percentage of their water supplies from stormwater. That would help make urban area much more resilient to aridification and drought. The local municipalities in the Bay Area, the greater Los Angeles metro, and the San Diego metro should not just rely on the state for funding on stormwater capture and recycling infrastructure but also add to the funding and expand the state funded projects. Referencing [6,7,8], 3 million acrefeet of water per year can serve Los Angeles County, Orange County, and San Bernardino County.

It is worth noting that urban runoff can contaminate water to a point where water treatment plants and wastewater recycling facilities are just not able to clean. We've seen two major incidents of spills in the United States in 2023 that jeopardized the drinking water, Philadelphia and East Palestine.

Greywater and Wastewater

In [5], California plans to incorporate additional capacity to recycle 800,000 acrefeet of gray and wastewater by 2030 and 1.8 million acrefeet by 2040. I don't have much else to say about greywater and wastewater recycling other than that municipalities should do the damned hardest to build the capacity to recycle for when precipitation happens and we can recycle any stormwater captured or detained.


  1. California Droughts
  2. What is CA doing to capture all this rainwater for a sunny day?
  3. Why The LA River Started California's Water War
  4. California Water Resilience Portfolio 2020
  5. 2022 Water Supply Strategy
  6. LADWP Fact Sheet
  7. Orange County Monthly Water Usage Data and Water Supply Info
  8. San Bernardino County Water Consumption

Wrapping Up the Blog Series With a Bow

This is the end of the blog series on the water reservoirs of California. My parting thoughts are that Californians should reach out to their representatives at the municipal, state, and federal level to support funding water infrastructure. Our state, the nation, and California's export markets depend on it. Here is an outline what policymakers can do right away:

  1. Municipalities should fund stormwater capture and detention infrastructure that can feed into wastewater facilities.
  2. The State should accelerate the timeline of their objectives in Gavin Newsom's Water Resilience Portfolio and 2022 Water Supply Strategy to quell any potential drought that ensues before 2030. i.e. The state assembly and senate should legislate and fund wastewater and stormwater projects to match the cadence of drought cycles and not arbitrary decadal timelines. Nature doesn't know what a decade is.
  3. House Representatives and Senators should add supplemental funding at the federal level to support the state and municipalities' stormwater and wastewater infrastructure initiatives.

The goal in the end is to make sure that the stormwater and wastewater facilities in California can integrate with California Water Supplies through the various water districts and water reservoir systems. The more storm and wastewater recycling capability California has, the better off Californians in the major metro areas will be in droughts and climate change's aridification this century.

As for agrarian Californians, we should consider more subsidies and investments in agrivoltaics and irrigation strategies that minimize flood irrigations that come from our water reservoirs and ground water.

Lastly is a table. For each reservoir and each water year, I identify the date of the highest acrefootage measurement and lowest acrefootage measurement. Note that for the most recent calendar year, the results may vary as the water year completes.