For more than eight decades, the Thomson family has worked to secure and responsibly manage water for agriculture in Los Carneros.

Historically a water-deficient agricultural region, Carneros has limited groundwater resources that must also serve the domestic and potable needs of rural residents. Beginning with surface-water planning 

In the 1940s and continuing through reclaimed water and precision irrigation today, four generations of the Thomson family have worked to reduce agriculture's dependence on potable groundwater. 

“We don't dry farm because we like it. We dry farm because we have to.” - M.A. Thomson Jr. 

As early as 1941, Thomson was studying the movement and availability of water across the property. Historical water-right records identify agriculture, domestic use, stock watering and fish among the property's water uses. Working with state and federal agencies including the Department of Natural Resources' Division of Water Resources, U.S. Army Corps of Engineers, federal soil-conservation programs, California Division of Fish and Game and Napa County Resource Conservation District, the family developed an integrated system of water and drainage infrastructure. 

In 1949 M.A. Thomson Sr. and Jennie Barnum Thomson applied for and were granted rights to pump from the Carneros Creek. In 1950, the Thomsons applied for and were granted a federal soil-conservation grant to construct a 31-acre-foot on stream agricultural reservoir in partnership with the U.S. Army Corps of Engineers, using their own heavy equipment and labor. 

The Division of Water Resources, State Engineers Edward Hyatt and A.D. Edmonston granted Thomson rights to pump, transfer, store water under two appropriative water right applications. 

Upon approving the applications, the State of California Department of Public Works, Division of Water Resources informed M.A. Thomson Sr. and Jennie Barnum Thomson that “fees are now due” in accordance with the Water Code. The damage: 28 acres at five cents per acre — $1.40. The Bureau of Fish Conservation, Division of Fish and Game was promptly notified of the projects. California water permitting, it seems, has changed a bit since the 1940s.

By the 1950s, the system was irrigating the family's orchards, helping size pears for the fresh-fruit and canning markets. That dependable water supply would later support the ranch's transition to winegrapes—and, ultimately, sparkling wine.

Thomson established the first irrigated orchards in Los Carneros.

As the ranch evolved from orchards to vineyards, Thomson continued investing in irrigation, drainage and water infrastructure. Between 1968 and 1971, M.A. Thomson worked with the Napa County Resource Conservation District and federal conservation engineers to develop Thomson Vineyards' first drip-irrigation system for winegrapes, adapting infrastructure established a generation earlier to a new crop.

In 1972, the family again worked with the U.S. Department of Agriculture Soil Conservation Service and the Napa County Soil Conservation District. Agricultural Engineer E. N. Burton designed the enlargement of the Thomson Reservoir, calling for approximately 6,400 cubic yards of excavation and four additional acre-feet of reservoir storage. The plan bears the agencies' review and approval.

It seems getting 6,400 cubic yards of excavation approved in Napa County has changed a bit since then, too.

Thomson again worked with the U.S. Department of Agriculture Soil Conservation Service and Napa County Resource Conservation District on agricultural drainage and erosion control in 1984. The conservation plan coordinated drainage across neighboring properties, including land owned by Doyle and Kathy Moon and the Sunnafrank Family, creating a connected system to carry water through a series of private lands and Napa County culverts to  Los Carneros Creek. The historical records reflect something farmers have long understood: water does not stop at property lines.

Today, tributaries connect the Thomson Ranch to Carneros Creek, the Napa River, San Pablo Bay and the greater San Francisco Bay watershed, making the Thomson on-stream reservoir a central component of the surrounding 149-acre Carneros watershed and its downstream habitat. 

The family's involvement in agricultural water eventually extended beyond the Thomson on-stream reservoir. 

Matthew A. Thomson Jr. was a founder of the Los Carneros Water District, formed in 1978 through a landowner-led effort to pursue alternatives to groundwater pumping and surface-water diversions. 

Decades later, reclaimed water would provide Carneros agriculture with another alternative to limited groundwater resources.

In 2013, Jennifer R. Thomson began serving on the Los Carneros Water District Board of Directors as the District was developing infrastructure to deliver reclaimed water for agricultural irrigation. 

Read More → Los Carneros Water District History

At Thomson Home Ranch, Jennifer began another generation of infrastructure improvements. In 2014, the mainline used to move water from Carneros Creek to the Thomson Reservoir was modernized, pump and electrical facilities updated and water metering added. 

When reclaimed water began flowing in 2016, the LiveWire Ranch was the second vineyard in the district to connect to the new LCWD system.  Nearly 7 acres was planted and automatic irrigation installed. Today, all Thomson Vineyards properties within Los Carneros are irrigated with LCWD water. 

Precision fertigation followed in 2018.

In 2026, Thomson is advancing that system again with automatic irrigation valves and advanced automated fertigation at Thomson Home Ranch.

In partnership with Simplot Grower Solutions & Water Logic and HotSpot AG, the specialized water-treatment and irrigation-management platform enables Thomson to remotely manage irrigation and fertigation while measuring and recording precise applications of water and nutrients. 

The new system will operate on existing and newly upgraded three-phase power supported by solar generation installed in 2025 on the original Thomson Cold-Storage Building.

The building appears on the 1909 Rancho Rincon de Los Carneros parcel map and has supported agricultural infrastructure on the property since the Thomson family began farming there in the 1930s. More than a century after it first appeared in the historical record, it is helping power the ranch's newest agricultural technology.