The buy-back has cost the city nearly €650 million, utilities giant RWE said on Tuesday, confirming it had sold its 24.95 percent share to the city authorities.
Shares in Berlin's water company were sold 13 years ago, leaving the city state with a majority holding of 50.1 percent.
Prices for consumers rose dramatically during the following years – and although the quality is generally considered to be very high, water prices in the capital are among the highest among German cities, the Tagesspiegel newspaper reported on Tuesday.
A city-wide vote two years ago exerted pressure on city politicians, as it showed a clear majority in favour of publishing the privatisation contracts, which are now being examined by a city parliamentary committee.
The vote also triggered the start of negotiations between RWE and the city, which ended with the sale of the quarter share for €618 million plus additional costs which brought the entire cost to €658 million.
The federal cartel office demanded a reduction in water costs of up to 18 percent this June. And although an appeal against this from the water company is still undecided, Berlin's Social Democrats pushed for the re-buy of the RWE shares.
The other remaining private shareholder is the French company Veolia, which has a share of 24.95 percent. Berlin is set to renegotiate its contract, the Tagesspiegel said, adding that the Social Democrats in the city were open to discussing buying the Veolia share.