Doulton Tunnel is a 2.2-mile long tunnel that conveys surface water from Jameson Lake through the Santa Ynez Mountains to the District's Bella Vista treatment plant.
Groundwater infiltration through Doulton Tunnel is a distinct and important source of water supply for the District. During consecutive years of normal rainfall, groundwater infiltration through the tunnel produces approximately 300 to 350 acre feet per year. This groundwater is commingled with surface water being conveyed from Jameson Lake, but is considered as a separate source; when no water is being delivered from Jameson Lake groundwater infiltration continues to flow through the tunnel. In fact, the water needs of the district were entirely supplied from Doulton tunnel between 1924 and 1927, before it was holed through to meet the reservoir.