Through evaporation, water enters the atmosphere. A breeze over the ocean moves the moist air inland. The result is rain but when sufficiently cooled the result is snow, more precisely a snow cap on the mountains. When the snow cap melts it gives rise to rivers, then ponds and lakes. The lakes may be man made or a reservoir, a dam if you will.
The stored water is distributed through canals, pipes and tunnels. This can be conveyed by gravity flow or by pumps. The water eventually reaches the end users in agriculture, industry and residences.
I personally do no have the data but I do not believe that God is making more water. Therefore water is endlessly being recycled in a natural way.
As I recall from my research in California there are two major reservoirs. One is Lake Shasta in Shasta County; the other is in Butte County. The former is the Federal reservoir built by the WPA during the Great Depression. It is known as the Central Valley Project. It was built to exclusively provide water to agriculture in the San Joaquin Valley. The other reservoir is the Oroville Dam; it was built to provide multiple use water, but especially for residential usage.