Rainfall over the past 10 days has caused severe flooding in many parts of Spain and on Tuesday the Met Office issued weather alerts for more than half the country.
Hydropower reservoirs held enough water to generate 9,425 gigawatt-hours, a jump of 685 GWh since last week, the Ministry for the Environment and Rural Affairs said in its latest weekly bulletin.
Data from national grid operator REE total demand over the past year in Spain was 251,600 GWh, so reserves would be enough to provide electricity for 13.7 days, if no other power sources were available.
In recent weeks hydroelectricity's share of the generation mix has recovered after months of near-drought and on Tuesday it helped drive down wholesale power prices to year-lows.
Greater availability of hydroelectricity makes Spain less dependent on generators fueled by gas, more than 99 percent of which it has to import.
Demand for gas fell by 9.3 percent in the year to November from the same period in 2008, according to gas grid operator Enagas.
Spain is also the world's third-largest importer of liquefied natural gas, via six regasification plants.
Rainfall logged by the Ministry was more than three times the historical average for the week to December 27, at 50.7 millimeters.
Reservoirs set aside for consumption, including irrigation, meanwhile leapt to 45.5 percent of capacity from 37.7 percent a week ago.
Irrigation is needed to grow maize and cut into Spain's hefty structural grain shortfall, which requires annual imports of at least 10 million tonnes from countries ranging from Argentina to Ukraine.
Farmers say weather conditions are currently ideal for planting cereals, but estimate they will sow about 5 percent less land this winter and spring due to low farm-gate prices.
Rice, cotton and alfalfa -- which is used in animal feed -- also need irrigation.
(Reporting by Martin Roberts; editing by James Jukwey)