MADRID, Dec 21 (Reuters) - Spain said on Tuesday it will repay power utilities 1.9 billion euros ($2.15 billion) after the Supreme Court ruled they had been unlawfully charged for the use of water. Utilities, including Iberdrola (IBE.MC), Acciona (ANA.MC) o Endesa (ELE.MC) and a unit of Portugal"s EDP (EDP.LS), had sued to recover a retroactive charge imposed in 2015 by the previous conservative government on hydro-power plants. Spain"s Supreme Court ruled in May that it was illegal to impose the levy, which was for 2013 and 2014, retroactively. Energy Minister Teresa Ribera said on Tuesday after the government"s weekly cabinet meeting that the charge "was considered illegal by the Supreme Court and it forces us to return what was charged for these years". Spain"s electricity system earned too little to cover its costs between 2000 and 2013, building up debts of more than 30 billion euros with government backing. Madrid introduced the hydro tax in 2015 as part of a bid to contain this so-called tariff deficit, which Spain"s competition watchdog said had reached 14.3 billion euros in 2020. ($1 = 0.8853 euros) Reporting by Emma Pinedo and Inti Landauro; Editing by Kirsten Donovan and Alexander Smith