* Hydropower capacity 14,823 GWh, down 318 GWh
* Irrigation reservoirs 76.6 pct full
* Wheat, barley harvest set to rise from 2010
MADRID (Reuters) - Spain has less water than a week ago to generate hydropower and irrigate crops, the latest official data showed on Tuesday, potentially adding to its already hefty burden of gas and grain imports.
The Ministry for the Environment and Rural Affairs said in its latest weekly bulletin that hydropower reservoirs had enough water to produce 14,823 gigawatt-hours of electricity, 318 less than last week.
With annual demand running at 259,000 GWh, hydropower stations could, by themselves, meet Spain's average electricity needs for 20.9 days.
Despite the drop, reserves were 22.1 percent above the average for the last ten years, a factor which has kept gas-fired plants idle and hobbled a recovery in gas demand in the world's eighth-biggest natural gas importer.
Vigorous hydro output also weighs on wholesale power prices and affects revenues for generators such as Iberdrola, Endesa, Gas Natural and Hidrocantabrico.
The Ministry recorded 2.2 millimeters of rainfall for the week ending on July 10, which was 50.2 percent of the historical (1930-96) average.
Rainfall in spring was adequate for Spain's wheat and barley crop, however, which has not suffered from the drought causing concern over northern European harvests.
Reservoirs set aside for irrigation, which is vital for growing maize in Spain, were down to 76.6 percent of capacity from 78.2 percent last week but comfortably above a 10-year average of 58.1 percent.
Even if farmers reap a bumper harvest, Spain still needs to import at least 7 million tonnes of grain a year to meet demand, which it buys from as far afield as Argentina and Kazakhstan.
(Reporting by Martin Roberts; editing by Keiron Henderson)