San Diego County's Natural Water Supply


Every Landscape Is Associated With A Watershed

A watershed is an area surrounded with a ridge (or divide) of land that separates water flowing to different rivers, streams, basins, lakes, or oceans. Each watershed has unique characteristics including:
  • geological features: bedrock, surface deposits (soils and alluvial deposits), fault and fracture systems that impact surface runoff and groundwater
  • climate/precipitation factors
  • environmental features: surface cover plant communities and habitats, and the wildlife they support
  • land use: urban/rural communities and developments, agriculture, highways/roads, mines, dams, sewers and wastewater treatment infrastructure, parks, power utilities, and other human-related activities and infrastructure.

Click on images for a larger view!

Rocky rapids on the Escondido River in Elfin Forest
Fig. 1. Escondido River flows through Elfin Forest Reserve.
San Diego County has 11 westward-draining watersheds (Figure 2). East of the county elevation divide along the crest of the Peninsular Ranges, the water drains eastward toward the Imperial Valley and Salton Sea.

Project Clean Water is an organization that provides a web-based portal to water quality and resource information for the San Diego County, South Orange County and South Riverside County.
Below are links to some of their watershed management area descriptions.
Santa Margarita
San Luis Rey
San Dieguito
Los Peñasquitos
Mission Bay/La Jolla
San Diego River
San Diego Bay
Fig. 2.
Map of watersheds in the San Diego County region.
Watersheds map of the San Diego County region

Who Manages Your Water?

The total "potable" (drinkable) water consumed in San Diego County for year 2018 was about 452,090.2 acre-feet. This water was distributed through 24 water districts under guidance by the San Diego County Water Authority.

What And Where Is Your Water District?

The San Diego County Water Authority oversees the distribution to member agencies (cities, water districts, and irrigation districts). In turn, these organizations distribute water to their communities, manage watershed areas (surface & groundwater supplies), and treat or recycle wastewater, etc.

1. Carlsbad Municipal Water District
2. City of Del Mar
3. City of Escondido Water Division
4. Fallbrook Public Utility District
5. Helix Water District
6. Lakeside Water District
7. City of National City (Sweetwater Authority)
8. City of Oceanside, Water Division
9. Olivenhein Municipal Water District
10. City of Otay
11. Padre Dam Municipal Water District
12. Marine Corps Base Camp Pendleton
13. City of Poway
14. Rainbow Municipal Water District
15. Ramona Municipal Water District
16. Rincon Del Diablo Municipal Water District
17. City of San Diego
18. Encinitas - San Dieguito Water District
19. Santa Fe Irrigation District
20. South Bay Irrigation District (Sweetwater)
21. Vallecitos Water District
22. Valley Center Municipal Water District
23. Vista Irrigation District
24. Yuima Municipal Water District

County of San Diego (East County region)
Fig. 3. Water Districts in San Diego County.
Map showing the location of 24 water districts in San Diego County.
Source: San Diego County Water Authority
Member Agency Map
Note: One of the most useful experiences you might ever get is to take a tour of the water district facilities for your community.
You might ask them for a job while you are at it!

Reservoirs of San Diego County

San Vicente City of San Diego 249,358
El Capitan San Diego 112,807
Henshaw Vista I.D. 51,774
Morena City of San Diego 50,694
Lower Otay City of San Diego 47067
Barrett City of San Diego 34,806
Sutherland City of San Diego 29,508
Sweetwater Sweetwater A. 28,079
Olivenhain SDCWA 24,774
Lake Hodges City of San Diego 13,401
Ramona Ramona M.W.D. 12,000
Jennings Helix W.D. 9,790
Cuyamaca Helix W.D. 8,195
Miramar City of San Diego 6,682
Murray City of San Diego 4,684
Poway City of Poway 3,432
Wohlford City of Escondido 2,783
Dixon City of Escondido 2,606
Turner Valley Center 1,612
Red Mountain Falbrook P.U.D. 1,335
San Dieguito Santa Fe I.D. 883
Maekle Carlsbad M.W.D. 600
Morro Hill Rainbow M.W.D. 465
TOTAL   722,735
Fig. 4. Map showing the location of the 12 largest water storage reservoirs in San Diego County.
Map showing the location of the 12 largest reservoirs in San Diego County.
These reservoirs are associated with different water districts that have their own rules about public access. Over time, public access to reservoirs have been growing increasingly restrictive, mainly for reasons for security, water quality safety, and habitat protection. For instance, the spread of invasive species by boaters, such as the zebra mussel, has been used to justify access restrictions.

None of the reservoirs are associated with natural lakes. However, some of the reservoirs are located in valleys or canyons associated with the regional fault system. For Example, Lake Henshaw is located in the rift valley of the Elsinore Fault (Figure 6).

San Diego's 10 largest Reservoirs

Fig. 5.
Satellite map of San Vicente and El Capitan Reservoirs, San Diego County's largest reservoirs.
San Vicente
(1) and El Capitan (2) Reservoirs: San Diego's two largest reservoirs.
Fig. 6.
View of the upland valley with Lake Henshaw as seen looking east from Palomar Mountain.
Lake Henshaw
(3rd largest) in the San Felipe Valley located in central northern San Diego County between Palomar Mountain to the west and the Volcan Mountains to the east.
Fig. 77.
Moleno Reservoir (4) and Lake Barrett (8) Reservoirs east of San Diego.Lake Molena (4) and Lake Barrett (6) Reservoirs east of San Diego.
Fig. 8.
Satellite map of Lower Otay Reservoir and Sweetwater Reservoir near San Diego.
Lower Otay (5) and Sweetwater (8) Reservoirs east of San Diego.
Fig. 9.
Lake Sutherland Reservoir located in the mountains near Ramona.
Lake Sutherland
(7) Reservoir near Ramona.

Fig. 10.
Olivenhein Reservoir in mountain valley above Lake Hodges. Water is pumped up to the reservoir and the released to generate electricity during peak demand periods.
Olivenhain Reservoir (9) in mountain valley above Lake Hodges near Escondido.
Fig. 11.
Satellite map of Lake Hodges and Olivenhein Reservoir southwest of Escondido.
Lake Hodges (10) and Olivenhain (9) Reservoir

Where Else Does San Diego Get Its Water Locally?

Think about all this water being imported into San Diego, and how much of it is being used to water landscapes. The amount of water being imported is more than all the largest natural rivers and stream in the county combined! It is no wonder that streams that otherwise would dry up during the dry season are now perennials streams. There are many new seeps in the sea cliffs along the coast as well. There is the equivalent of a whole new river flowing into San Diego County!

Actually only a small percentage of the water supply in San Diego currently comes from wells (groundwater resources). Groundwater drains form upland regions drains into local streams. Reservoirs may trap this water, but leakage from reservoirs also adds to groundwater. There is probably much more groundwater flowing directly into the ocean than from surface runoff from San Diego's rivers and streams.

Seawater desalination and salty groundwater reclamation are now contributing about 10% of San Diego's drinking water supply, and that amount is expected to grow as new projects come online.

Cities throughout San Diego County are now "recycling" water - treating sewage and urban runoff so it can be used for irrigation in parks, schools, golf courses, landscaping along roads and highways, and local agriculture projects. In the future, a large amount of drinking water will come from recycled water. This technology is supplying drinking water in many other parts of the world, and will no doubt be a significant source of California's drinking water in the future.

Other water saving will come through increased conservation practices (of which there are many!).


Water Treatment, Storage, and Distribution Infrastructure

Perhaps the most important (and expensive) parts of the water delivery system is all the infrastructure necessary to purify, fluoridate, store, and distribute water to all the residents within a water district.

According to a 10-News report in 2018, the City of San Diego water system extends over 400 square miles and moves about 172 million gallons of water per day (527.6 acre feet). Within this network there are 49 water pumping stations, 29 treated water storage facilities, three water treatment plants, and more than 3,300 miles of pipeline. All this infrastructure needs maintenance and eventual replacement. Some of the pipes are 100 years old. Water lines connect to more than a million households. Fire hydrants are spaced about 300 feet apart (but no more the 600 feet apart) in residential and commercially zoned areas.
Fig. 12.
Tow large underground water storage tanks covered with solar panels with mountains in the background. Twin Oaks Water Treatment Plant is underground in the foothills near San Marcos completed in 2018 is one of the world's largest.

Fig. 13.
View inside the Twin Oak undeground water storage tank.
View inside the massive Twin Oaks water treatment tank

Fig. 14.
Water tank on Double Peak in San Marcos
Water storage tank like this one on top of Double Peak in San Marcos are used to maintain daily water supply.

Continue to the next page (a tour of the San Dieguito River Watershed).

A) Where Does San Diego Get Its Water?
B) The Colorado River Drainage Basin
C) California's Interconnected Water System
D) San Diego County's Natural Water Supply
E) The San Dieguito River Watershed
F) Water Conservation
G) Assignment Tasks & Questions