The storms that doused Los Angeles County over the weekend filled reservoirs in the San Gabriel Mountains with some 6 billion gallons of water, enough to supply more than 150,000 people for a year.
The twin storms left more than 11 inches of rain in some higher elevations.
The rainfall from the storms was enough to substantially fill some dams that were at minimum levels, according to the Los Angeles County Department of Public Works, which operates 14 dams and debris basins in local ranges.
Cogswell Dam on the San Gabriel River rose by 36 feet immediately after the storm. Larger dams farther down the river rose by lesser amounts, the agency said.
The water in the dams is not the most relevant measure of available resources, officials say, because the county sends dammed water into spreading grounds that recharge underground aquifers.
The largest spreading grounds operated by the county are near the mouth of San Gabriel Canyon, where the 10 Freeway crosses the 605 Freeway. The water slowly percolates into the ground, where it can be stored to be pumped out later.
About one-third of the water supply for Southern California comes from groundwater resources that are mostly managed from mountain runoff.
Despite the windfall of rainwater from the storms, the county is still far short of the 210,000 acre-feet or 68 billion gallons that it usually captures in a rainy season.
Local water officials have warned that they may have to reduce allocations to local water districts starting in July, based on the low rainfall so far. The groundwater basins are controlled by water masters who dole out water under legal agreements struck decades ago.
Next month, for example, engineers will examine the level of a key well in Baldwin Park to make one of their determinations.
Until the most recent storms, that well was 16 feet below last year's level.